ExxonMobil topped the list at $344,500 in contributions, $304,500 of which went to Republicans.

Koch Industries, owned by the billionaire brothers who have often backed conservative candidates and causes, came in second by giving $297,000 to Republicans and $5,000 to Democrats.

Rounding out the top five were Marathon Petroleum ($226,000), Halliburton ($161,500) and Chevron ($153,501).

The mining industry has also heavily favored Republicans, giving 83 percent of a total $476,000 in donations to GOP candidates.

The Electric utility industry was less skewed toward Republicans. Such PACs have contributed $3.1 million, handing checks to GOP candidates two-thirds of the time.