Corporate giants are making big contributions to disaster relief organizations to help victims of Tropical Storm Harvey.

The storm is expected to leave behind billions of dollars in damages.

Companies have pledged $65 million to relief efforts as of late Wednesday morning, according to an estimate from the U.S. Chamber of Commerce. But this figure is constantly changing as contributions continue to pour in.

CNNMoney's analysis found that 30 companies had donated $1 million or more by Wednesday morning. Verizon alone contributed $10 million on Tuesday.

Meanwhile, employee donation matching programs announced so far could bring in an additional $3.6 million. This figure will likely climb, as some companies left the amount they would match open ended, while others are also accepting customer donations.

Related: Impact Your World - How you can help

"The corporate response thus far [has] been strong," Marc DeCourcey, senior vice president of the Chamber of Commerce Foundation, told CNNMoney.

However, it's still too soon to tell how corporate donations to Harvey compare to other disasters.

"This disaster is still unfolding. ... We're still in the response phase, and in some instances the rescue phase. We're encouraging companies all across America to give now, and to give to trusted nonprofits," DeCourcey said.

Related: How much damage will Harvey cause?

In 2005, Hurricane Katrina and Rita in 2005 brought in more than $1 billion in business aid within the first six months of each disaster, according to the Chamber of Commerce Center for Corporate Citizenship.

The Indian Ocean tsunami in 2004 raised $566 million from corporate donations, while the 2011 Japanese earthquake and tsunami brought in $301 million. Hurricane Sandy in 2012 raised $141 million within the first six months in business aid, per the Chamber's data.

Companies have also gone beyond just writing a check, such as volunteering, providing in-kind donations like water and food, and encouraging employees to donate by matching contributions, according to Mark Shamley, the president and CEO of the Association of Corporate Citizenship Professionals.

"The bottom line is companies have embraced their civic duty to respond to disasters in ways that transcend check writing," he said.

When companies respond to disasters, they build a tremendous amount of good will externally and internally, says Una Osili, associate dean at the Indiana University Lilly Family School of Philanthropy.

"Employees themselves want to work within companies that are engaged in a broader social good and making the community better," she said.

As Harvey pummels Texas, many corporate giants are overwhelmingly donating to the Red Cross.

"While it is too early to compare this disaster to any others from a financial perspective, we can say that we are extremely pleased and gratified by the outpouring of support we are receiving to help those affected," a Red Cross spokeswoman told CNNMoney.

Here's a running list of what companies are doing to help.

Abbott

Abbott (ABT) and its foundation the Abbott Fund are giving $1 million in grants and healthcare and nutrition products. That includes $900,000 in grants to the Red Cross, Americares and Direct Relief, and $100,000 in healthcare and nutrition products.

Aetna

The Aetna Foundation (AET) announced a $100,000 contribution to both the American Red Cross and the Community Foundation of Greater Houston. It will also donate $50,000 to nonprofit Team Rubicon to assist current and future disaster relief efforts.

Allergan

The Allergan Foundation (AGN) on Monday said it will donate $100,000 to the Red Cross to support victims of Harvey.

Amazon

Amazon (AMZN) and Whole Foods will match cash donations made on Amazon.com up to $1 million to the Red Cross Hurricane Harvey Relief.

American Express

American Express (AXP) is donating $150,000 to the Red Cross. It will match up to $100,000 in employee donations to the Red Cross.

Amgen

Amgen (AMGN), a biopharmaceutical company, is donating $80,000 to Direct Relief International and $20,000 to the American Kidney Fund's Disaster Relief Program to help dialysis patients impacted by the storm.

The company will also match employee donations.

Apple

The tech giant made a $2 million donation to the Red Cross over the weekend, an Apple spokeswoman told CNNMoney. Apple (AAPL) will also match employee donations 2 to 1. Users can donate to the Red Cross through iTunes or on the App Store.

AT&T

AT&T (T) is contributing $350,000 to help communities following the storm, including $100,000 to the Greater Houston Community Fund, $100,000 to the Red Cross Hurricane Harvey Fund and $50,000 to the Coastal Bend Community Foundation in South Texas.

The AT&T Foundation will match employee donations up to $50,000 each to Team Rubicon and to the AT&T Employee Disaster Relief Fund, which supports employees who live in the areas affected by the storm. (AT&T is acquiring Time Warner, the parent company of CNN.)

Bank of America

The Bank of America Charitable Foundation is donating $1 million to support Harvey relief efforts, including a $250,000 donation to the Red Cross. The remainder of the funds will be allocated as the company learns more about recovery needs, a spokesperson told CNNMoney.

Bank of America (BAC) will also match employee donations of $1 or more until September 30. Its usual gift match minimum is $25.

Bayer

Bayer told CNNMoney it is donating $100,000 each to the Red Cross and nonprofit Direct Relief.

BB&T

Bank BB&T (BBT) is giving $100,000 to the Red Cross of Greater Houston in Texas.

BBVA Compass

BBVA Compass' foundation will contribute $250,000 to the Red Cross and the Hurricane Harvey Relief Fund.

The bank also aims to raise up to $250,000, both online and at its branches, from employees and customers for those organizations.

Boeing

The Boeing Charitable Trust (BA) committed $1 million to the Red Cross for Harvey relief efforts.

BMO Financial

Financial services provider BMO Financial contributed $100,000 to the Red Cross.

BP

BP and the BP Foundation have donated $750,000 to assist with relief efforts. The contribution will be split equally among the Red Cross, the Community Foundation of Greater Houston and the United Way of Greater Houston.

The company will also match employee contributions.

Caterpillar

The Caterpillar Foundation (CAT) donated $300,000 to the Red Cross to help with immediate relief efforts for Harvey.

Cheniere Energy

Cheniere Energy (LNG) on Monday said it will make a $1 million donation to the Red Cross to help with relief and recovery efforts following the storm.

Chevron

Chevron (CVX) is making a $1 million donation to the Red Cross. The oil and gas company will also match donations made to relief efforts by its employees and retirees.

Cigna

The Cigna Foundation is contributing $100,000 to the Red Cross. Cigna (CI) employees can also request matching funds for their donations to the Red Cross.

Citi

The Citi Foundation (C) has committed a $1 million donation to the Red Cross, the company told CNNMoney.

Coach

The Coach Foundation has committed $200,000 to the Red Cross. Coach (COH) will also match employee contributions.

Coca-Cola

The Coca-Cola Foundation pledged $1 million to the Red Cross on Tuesday. Coca-Cola (KO) will also match employee donations made to the company's Employee Disaster Relief Fund up to $100,000.

Comcast

Comcast NBCUniversal (CMCSA) is giving $500,000 toward the Houston Mayors' Hurricane Harvey Relief Fund and the Red Cross. The organizations will share the donation.

The company will also donate advertising time on its cable networks to these organizations to run public service announcements about how to aid with flood relief efforts.

Comerica

Comerica (CMA), a Dallas-based bank, will donate $100,000 to the Red Cross.

ConocoPhillips

ConocoPhillips is making a $1 million donation to the Red Cross. Employees and retirees in the U.S. can request to have their personal contributions matched.

CVS

CVS Health and the CVS Health Foundation announced $200,000 in cash and in-kind product donations, including $50,000 each to the Greater Houston Community Foundation and the Red Cross, and $25,000 to the Salvation Army.

CVS (CVS) will also match employee contributions up to $25,000.

Discover

Discover (DFS) will match donations up to $500,000 for every cardholder who donates to the Red Cross via their Cashback Bonus program or makes a donation with a Discover card. The company is also matching employee donations.

Disney

Disney (DIS) and ABC's Houston TV station KTRK-TV announced a $1 million contribution to the Red Cross. The company is matching employee donations.

Dollar General

Dollar General (DG) is donating $50,000 to the Red Cross. Customers can also make a contribution in stores through September 9.

Dow

The Dow Chemical Company Foundation is contributing $1 million to support Harvey relief, including $100,000 each to the Red Cross Disaster Relief Fund and Team Rubicon.

Dow (DOW) is also matching employee and retiree donations up to $100,000 to the Red Cross.

Enterprise Rent-A-Car

The Enterprise Rent-A-Car Foundation is donating $1 million to the Red Cross.

Exelon

Exelon (EXC) is donating $150,000 to the Red Cross. The utility company will also match employee contributions up to $5,000 per person.

Exxon Mobil

Exxon Mobil (XOM) on Friday said it's donating $500,000 to Red Cross organizations along the U.S. Gulf Coast to aid with relief efforts. On Tuesday, the company contributed $500,000 to the United Way of Greater Houston.

Facebook

Facebook (FB) will match up to $1 million in donations made on its platform for the Center for Disaster Philanthropy's Hurricane Harvey Recovery Fund.

FedEx

FedEx (FDX)committed $1 million in cash and transportation support to deliver medical aid and supplies in the wake of the storm. It works with the Red Cross, Direct Relief, Heart to Heart International, the Salvation Army and Team Rubicon.

Ford

The Ford Motor Company Fund (F) is donating $100,000 to disaster relief efforts in Texas. It will also match up to $50,000 in contributions to the Red Cross.

General Electric

The GE Foundation (GE) has donated $500,000 to the Red Cross, a spokeswoman told CNNMoney. It will also match employee donations to participating disaster relief organizations.

Google

Google (GOOG) is making a $250,000 Google.org grant to the Red Cross and matching employee donations up to $250,000. Google.org also launched a matching campaign for consumers, up to $1 million.

H-E-B Grocery

H‑E‑B Grocery will donate $100,000 toward Hurricane Harvey relief efforts, specifically to the Red Cross, Salvation Army and Feeding Texas. Customers can also make a donation at its Texas stores.

HCA Healthcare

HCA Healthcare (HCA) donated $1 million to the American Red Cross.

Home Depot

Home Depot (HD) on Monday committed $1 million to help storm relief efforts. The donation will go to nonprofits, such as the Red Cross, Salvation Army, Convoy of Hope, Operation Blessing and Team Rubicon.

Humana

The Humana Foundation, the philanthropic arm of health insurance company Humana, (HUM) on Saturday gave a $250,000 immediate grant to the Red Cross.

Intercontinental Exchange

Intercontinental Exchange (ICE) is making a $1 million contribution to the Red Cross and matching employee donations.

Jefferies

Investment bank Jefferies will donate $1 million to several charities aiding in the relief effort. The firm will also donate all net trading commissions on Wednesday from U.S., European and Asia equity, fixed income and foreign exchange trading to relief efforts.

JPMorgan

JPMorgan Chase (JPM) said it would donate $1 million to the Red Cross and other nonprofit groups providing immediate relief. The firm is also matching employee donations to these organizations.

Chase will also automatically waive or refund fees, such as late fees for mortgages and credit cards, through September 10 for customers in areas severely impacted by the hurricane.

Kansas City Southern

Kansas City Southern (KSU) said its charitable fund will donate $50,000 to the Red Cross. The railroad company will also match employee gifts up to $25,000.

Kellogg

Kellogg Company Fund, the charitable arm of Kellogg (K), is committing $100,000 to nonprofit Feeding America to aid disaster relief efforts.

Kindred Healthcare

Kindred Healthcare (KND) is making a $50,000 donation to the Red Cross to aid recovery efforts from Harvey in Texas and the Gulf Coast.

Kohl's

Kohl's (KSS)announced a $500,000 donation to the Red Cross. The department store will also give an estimated $1 million to help Kohl's associates who were significantly affected by the storm.

Kroger

The Kroger Co. Foundation (KR) committed $100,000 to the Houston Food Bank. For every share of Kroger's Facebook post, the foundation will donate $5 to the Food Bank, up to $100,000.

Lennar

Lennar (LEN) donated $1 million to the United Way of Greater Houston Flood Relief Fund. The homebuilding company will also match employee contributions.

Lowe's

The home improvement retailer on Saturday announced a $500,000 contribution to American Red Cross Disaster Relief to help provide food, shelter and supplies to those impacted by Harvey and other crises.

At Lowe's (LOW) stores in Texas, customers can also make a donation to the Red Cross.

Microsoft

Microsoft (MSFT) on Monday announced a $100,000 grant to the Red Cross.

MillerCoors

MillerCoors is pledging at least $25,000 to the Red Cross. The company also sent 50,000 cans of drinking water to Texas, where they will be distributed by the Red Cross.

Motiva

Motiva, a Houston-based oil company, pledged $500,000 to organizations such as the Houston mayor's Hurricane Harvey Disaster Relief Fund and the Red Cross.

New York Life

New York Life is donating $500,000 to support Harvey relief efforts, including $150,000 to the Red Cross and $100,000 apiece to Save the Children and Feeding Texas.

The life insurance company will also match employee donations up to $150,000 to these organizations.

NextEra Energy

NextEra Energy (NEE) is contributing $100,000 to the Red Cross and will match employee donations up to $100,000.

PenFed Credit Union

PenFed, one of the country's largest credit unions, will donate $50,000 to the Red Cross Corpus Christi and Houston chapters.

PepsiCo

PepsiCo (PEP) and the PepsiCo Foundation gave a $1 million grant to the Red Cross.

PetSmart

PetSmart Charities is giving $1 million to help animal welfare agencies that are working to rescue, relocate and care for pets that have become homeless due to the storm. These organizations include the Houston SPCA, the SPCA of Texas, Rescue Bank and Houston PetSet.

The company is also providing in-kind donations, like pet food and supplies.

PG&E

Pacific Gas and Electric Company (PG&E) (PCG) will match employee donations up to $50,000.

Phillips 66

Phillips 66 (PSX) will contribute $1 million to the Red Cross. The oil company will also match employee contributions up to $15,000 per person.

PNC

The PNC Foundation, the philanthropic arm of PNC (PNC) bank, will contribute $250,000 to the Red Cross and match employee donations up to $100,000.

Range Resources

Oil and gas company Range Resources announced a $100,000 donation to the Red Cross for Harvey relief aid.

Regions Bank

Regions Bank (RF) is donating $100,000 to support relief efforts. The funds will be split between the United Way of Greater Houston's Flood Relief Fund and a program to help Regions associates directly impacted by the flooding.

Ross Stores

Ross Stores (ROST) made a $400,000 donation to the Red Cross. The discount retailer is also accepting customer contributions in stores until September 16.

Samsung

Several of Samsung's U.S. subsidiaries are donating $500,000 to the Red Cross. The company is also giving $500,000 worth of products, such as washing machines, dryers, laptops and tablets, to nonprofits.

Sealed Air

Sealed Air (SEE) is making a $100,000 donation to the Red Cross. The company will also match employee contributions up to $25,000.

Sempra Energy

The Sempra Energy Foundation (SRE) will contribute $75,000 each to the Red Cross Hurricane Harvey Relief Fund and nonprofit Americares. The foundation will also match up to $50,000 in employee donations.

Shell

Shell (RDSA) announced a $1 million donation to the Red Cross Hurricane Harvey disaster relief fund on Tuesday.

Southern Company

The Southern Company Charitable Foundation (SO) will give $100,000 to the Red Cross. The company will also match employee and retiree donations.

Stanley Black & Decker

Stanley Black & Decker (SWK) announced a commitment of up to $125,000 for immediate disaster relief, including a $50,000 donation to the Red Cross and $25,000 to the Houston ToolBank. It will also match employee donations 2 to 1.

Starbucks

The Starbucks Foundation donated $250,000 to the Red Cross. Customers can also make a contribution to Harvey relief efforts at any Starbucks (SBUX) store in the U.S.

Stream Energy

Stream, a Dallas-based home energy and wireless provider, donated $25,000 through its philanthropic arm Stream Cares to the Red Cross Disaster Relief Fund.

SunTrust

The SunTrust Foundation (STI) announced a $100,000 grant to the Red Cross.

Target

Target (TGT) is donating $500,000 to support Harvey recovery efforts, including to organizations like the Red Cross, Salvation Army and Team Rubicon.

Taylor Morrison

Homebuilder Taylor Morrison (TMHC) has donated a combined $250,000 to the Red Cross Harvey Fund and to an internal Harvey relief fund. It will also match employee contributions.

Tenet Healthcare

Tenet Healthcare Foundation (THC) contributed $20,000 to the Red Cross.

Under Armour

Under Armour (UA) donated $50,000 to assist Team Rubicon in response to Harvey.

Union Pacific

Union Pacific (UNP) has pledged $250,000 to support Hurricane Harvey relief efforts, including $100,000 to the Red Cross and $50,000 to Houston Mayor Sylvester Turner's Hurricane Harvey Relief Fund.

The railroad company will match contributions to its employee support network through September 30, up to $100,000. It will also match donations made to the Disaster Relief Matching Gifts Program for Hurricane Harvey, where employees can contribute funding to the Red Cross, Salvation Army and other groups.

UnitedHealth

UnitedHealth (UNH) announced a donation of $1 million to support Texas communities impacted by the storm. The company said it's working with officials and stakeholders in Texas to determine "how the funds can most effectively support relief efforts."

It is also offering a 2 to 1 match for employee donations toward disaster relief efforts.

United Airlines

The airline will give up to three million bonus miles to MileagePlus members who donate to disaster relief organizations such as the Red Cross or AmeriCares. United (UAL) will also match the first $200,000 raised in donations on its crowdfunding campaign.

UPS

The UPS Foundation has pledged $1 million to Harvey relief efforts. This includes a combination of cash grants, in-kind transportation donations and technical expertise.

UPS (UPS) will donate an additional $500,000 in cash and assistance for the post-crisis recovery phase in the coming months.

Verizon

Verizon (VZ) pledged $10 million to support Harvey relief efforts. The company said it would share which nonprofits its donating to in the coming days.

Walgreens

Walgreens (WBA) pledged $200,000 to the Red Cross. Customers can also make a donation in stores in the U.S., Puerto Rico and U.S. Virgin Islands.

Walmart

Walmart (WMT) and the Walmart Foundation said they would give cash and product donations of at least $1 million to organizations like the Red Cross, Salvation Army and Convoy of Hope.

Waste Management

Waste Management (WM) announced a $3 million donation to various organizations, including the Houston Mayor's Fund and the Red Cross.

Wells Fargo

Wells Fargo (WFC) is donating $500,000 to both the Red Cross Disaster Relief Fund and to local nonprofits focused on relief efforts in Texas.

Western Union

The money transfer company's foundation announced a $30,000 donation to the Red Cross on Sunday. The Western Union Foundation will also match "qualifying" contributions from its agents.

Western Union (WU) will also provide free money transfers when users send funds to Texas from the U.S.