___No. 4: Robert Rowling, 58, head of Dallas-based TRT Holdings. Total: $5.1 million Rowling has given at least $5.1 million to Republican Party and candidates this election. Most of his contributions, $5 million, went to Rove's American Crossroads, both through personal donations and through his firm. Rowling also has given $100,000 to the pro-Romney Restore Our Future super PAC. Rowling's holdings are worth an estimated $4.8 billion and include Omni Hotels, Gold's Gym and Tana Exploration, his family's oil company. Rowling once told the Texas Tribune he prefers political donations to lobbying efforts. Rowling has been a big donor in Texas political circles, winning a role for Omni as operator of Dallas' convention center hotel after a 2009 city referendum fight. ___ No. 5: William Koch, 72, an industrialist whose South Florida-based energy and mining conglomerate is worth an estimated $4 billion. Total: $4 million Koch has given $4 million to the Restore Our Future, including a $250,000 personal donation and $3.75 million through his corporation, Oxbow Carbon LLC, and a subsidiary, Huron Carbon.Â Oxbow's latest $1 million donation to the pro-Romney committee was listed Friday. Unlike his brothers, Charles and David Koch, who are longtime supporters of Republican and conservative causes, Bill Koch has funded both GOP and Democratic Party candidates in the past. Koch's corporate interests have repeatedly battled against what company officials have decried as government interference. Oxbow spent $570,000 last year on lobbying in Washington, mostly aimed at mining, safety issues and climate change. The company has complained in federal filings about government delays on permits and has raised concerns about administration changes in regulations that would aid collective bargaining. Koch also has pushed for approval of the Central Rockies Land Exchange, a proposed swap of land tracts in Colorado and Utah to enlarge his 4,500-acre Bear Ranch. The proposal, which requires congressional approval, has sparked local opposition.