NEW YORK (CNNMoney.com) -- Oil rigs are leaving the Gulf of Mexico in record numbers, threatening to put upward pressure on U.S. oil and natural gas prices, according to a report published Wednesday.

Drilling companies are increasingly signing long-term deals with oil firms to send their rigs to more promising drilling regions overseas, said the Wall Street Journal.

Houston's GlobalSantaFe, for instance, agreed to a deal to send four rigs from the Gulf of Mexico to the the Persian Gulf to serve Aramco, the Saudi national oil company, said the report.

Many of the easily reached oil reserves in the Gulf of Mexico have already been drilled, while new prospects are being discovered off Africa, the Middle East and China.

Natural gas is mostly a local market, so decreased U.S. supplies won't be easily offset by international imports, said the Journal. Oil is a global commodity, so the impact of the departing rigs on American oil prices will be less.

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