Two top McCain aides said the decision could be announced after likely Democratic challenger Sen. Barak Obama of Illinois returns Sunday from Europe and before the start of the Beijing Olympics Aug. 8, The Washington Post reported Friday.

"He's in a position to make (the decision) on short notice if he wanted to," said Charles R. Black Jr., one of McCain's key political advisers.

Aides to the most likely candidates to join McCain on the ticket, provided "no comment" responses when to questions about whether they been asked to supply documents for vetting purposes, the Post said.

The short list includes former Massachusetts Gov. Mitt Romney, Minnesota Gov. Tim Pawlenty, Louisiana Gov. Bobby Jindal, former U.S. budget director Rob Portman and former Pennsylvania Gov. Tom Ridge, the Post said.