By Siobhan Hughes Of DOW JONES NEWSWIRES WASHINGTON (Dow Jones)--About two dozen U.S. Senators on Thursday asked Transocean Ltd. (RIG) to postpone making a dividend payment "until the extent of your company's responsibility" for a two-month-old oil spill in the Gulf of Mexico has been evaluated. The letter to Transocean Chief Executive Steve Newman comes after BP PLC (BP, BP. LN) has already canceled its dividend for the rest of the year after agreeing to contribute $20 billion to a spill-damage fund at the urging of the White House. Oil is still gushing out of a broken BP pipe in the Gulf of Mexico after the April 20 explosion of a rig that BP was leasing from Transocean. "In the face of such destruction, we urge you to follow the lead of BP and postpone your pending $1 billion shareholder dividend until the extent of your company's responsibility for the worst environmental disaster in American history is assessed," according to the June 24 letter. Transocean couldn't immediately be reached for comment. The letter was signed by Sen. Chuck Schumer (D., N.Y.), Sen. Mark Begich (D., Alaska), Sen. Patty Murray (D., Wash.), and Sen. Patrick Leahy (D., Vt.), among others. The lawmakers noted that they have already expressed concern about the dividend to U.S. Attorney General Eric Holder, who was one of the Obama administration officials present during White House negotiations with BP on the $20 billion escrow fund. "The legal proceedings around the disaster remain murky," the lawmakers wrote. "It seems inexplicable to us that, while a full accounting of your company's financial responsibilities is not yet clear, you are still planning to issue $1 billion in dividends as if no accident had occurred." The lawmakers also renewed expressions of concern about Transocean's efforts to limit its liability. Transocean, the owner and operator of the Deepwater Horizon rig, filed last month under the Limitation of Liability Act of 1851 to limit its liability to just under $27 million. -By Siobhan Hughes, Dow Jones Newswires; (202) 862-6654; [email protected] (END) Dow Jones Newswires June 24, 2010 19:08 ET (23:08 GMT)