NEW YORK (CNNMoney.com) - Chrysler's chief spokesman, Jason Vines, took on major oil companies Monday, saying they had failed to combat high gas prices, demonstrating outright greed.

Vines' blog posting reflected rising tensions between auto makers and the oil industry over stagnating vehicle fuel economy and high gas prices. Auto makers have not generally commented publicly on friction with the oil industry.

"Big Oil would rather fill the pockets of its executives and shareholders, rather than spend sufficient amounts to reduce the price of fuel, letting consumers, during tough economic times, pick up the tab," he wrote on an official Chrysler blog, thefirehouse.biz, which is open only to automotive journalists and industry analysts.

The piece was in response to an ExxonMobil ad alleging that the American automobile industry had not improved efficiency over the last 20 years, he said.

"Every form of transportation - planes, trains and automobiles - now benefits from improved fuels and engine systems," reads the ad, which began to run in print publications in late 2005. "So why is it that despite this overall progress, the average fuel economy of American cars is unchanged in two decades?"

Engine efficiency gains had been offset by the increasing size of vehicles, Exxon said.

Vines countered that "automakers have spent billions developing cleaner, more efficient technologies such as high-feature engines, hybrid powertrains, multi-displacement systems, flexible fuel vehicles and fuel cells."

The average fuel economy of American vehicles is now 21 miles per gallon, up from 13.1 miles per gallon in 1975, he wrote.

Vines also said that oil companies had favored paying executives and shareholders lavishly rather than invest in research and new refineries.

Exxon countered that it partners with several automakers on research to improve energy efficiency.

"One of these partnerships is with DaimlerChrysler to develop new lubricants to improve fuel economy, extend oil change intervals and lower emissions," said an ExxonMobil spokesperson in an e-mail.

DaimlerChrysler is the parent company of Chrysler.

Gas prices have severely impacted the sales of sport utility vehicles in recent years, which are among the auto industry's most profitable produtcs.

Related:

Fuel-efficiency gains offset by performance, size