A key measure of U.S. airline industry revenue slipped more than expected in October, pressured by excess capacity, weak demand and a lingering impact from hurricanes in Florida, analysts said.

Systemwide unit revenue, also known as revenue per available seat mile (search) or RASM, declined 2.9 percent in October from a year earlier, according to Wall Street analysts who receive the data from the Air Transport Association (search), an industry trade group.

The unit revenue slip occurred as capacity, or available seat miles, rose 4.8 percent during the month.

"Results likely (were) driven by excess capacity, weak demand and spill effect from a rough hurricane season," wrote Gary Chase, an airline analyst at Lehman Brothers (LEH), in a research note.

Earlier this month, Continental Airlines Inc. (CAL) estimated that its mainline unit revenue rose between 0.5 and 1.5 percent in October. Analysts use unit revenue figures from Continental, normally the only carrier that releases estimates at the start of the month, to predict unit revenue performance across the industry.

"Given an increasingly steep booking curve, we would have expected early October fare increases to translate into improved October revenue. We were mistaken," wrote Jamie Baker, J.P. Morgan analyst, in a research note.

"However, based on carrier feedback, we remain optimistic that November results will show evidence of improved pricing traction," he said.

Many airlines cited high oil prices as a leading contributor to financial losses in the third quarter. U.S. crude oil futures have weakened from a record high of $55.67 a barrel reached on Oct. 25 to trade near $46.60 on Thursday.