U.S. Sen. Mark Pryor, D-Ark., has amassed nearly $4 million for his re-election campaign, which is expected to be among the most hard fought in the nation.

Pryor appears to hold nearly a four-to-one cash advantage over his most likely challenger. Rep. Tom Cotton, R-Dardanelle, has just over $1 million cash on hand at the end of the second quarter.

Cotton raised $611,000 during the three-month period while Pryor raised more than $1.2 million, their respective campaigns announced Monday.

Cotton has not announced a candidacy for the Senate but is being urged by some state and national Republicans to challenge Pryor in 2014.

The three other House members already filed their second quarter reports with the Federal Election Commission.

Rep. Tim Griffin, R-Little Rock, reported raising $272,600 from April through June, and closed the second quarter with $447,334 cash on hand. He also had $34,666 in debts.

Rep. Steve Womack, R-Rogers, reported raising $123,427 and had $578,971 cash on hand.

Rep. Rick Crawford, R-Jonesboro, reported raising $99,186 and had $168,932 cash on hand.