Wallop, a Republican, was 78.
As a senator from 1977 to 1995, he gained a reputation for his work on energy and environmental policy affecting Wyoming, a state rich with oil, natural gas, coal and uranium, Roll Call reported.
"He's been ill for some time, but he has had a very active life and made a great deal of difference in this body," Enzi said on the Senate floor. "For all of his three terms, he was a powerful and effective presence in the Congress that ensured people of Wyoming that they were heard and that their concerns were being addressed."
In 1992, Wallop became the ranking member of the Energy and Natural Resources Committee, where he joined with Chairman J. Bennett Johnston, D-La., to help win passage of an energy plan offering incentives for conservation, opening electric utility markets and providing tax relief for oil and gas drillers, Roll Call said.
"It is nothing short of miraculous, the number of interests that have come together in this," Wallop said at the time.
Wallop, who was a rancher and meatpacking executive before being elected to public office, wore cowboy outfits and rode horses in campaign ads.
He also served two terms in the Wyoming House and one in the state Senate.
Wallop is survived by his wife, Isabel, and four children.