Delta Air Lines , the world's biggest air carrier, reported a narrower fourth-quarter loss on Tuesday as cost cuts outweighed revenue pressures.

But excluding merger-related expenses and other special items, the loss was wider than Wall Street expected, and Delta shares fell in premarket trade.

The company, which acquired Northwest Airlines in 2008, expects positive improvement in revenue per available seat mile (RASM) each month of this year as the recovery takes hold.

Delta posted a net loss of $25 million, or 3 cents a share, for the fourth quarter, compared with a loss of $1.44 billion, or $2.11 a share, a year earlier.

Excluding items, Delta's loss for the latest period came to $225 million, or 27 cents a share. On this basis, analysts on average expected a loss of 24 cents, according to Thomson Reuters I/B/E/S.

Operating revenue rose 1 percent to $6.8 billion in the quarter while operating expenses fell 12 percent.

Airlines have cut jobs and curbed capacity in the past two years in a bid to offset declining revenue as the recession battered business and consumer demand for air travel.

Last week, rivals Continental Airlines and Southwest Airlines posted improved quarterly profit performance and noted that business travel trends were picking up.

In a statement, Delta said revenue showed signs of recovery with increased corporate travel demand and monthly revenue improvement.

Delta shares were off about 3.6 percent to $12.85 in premarket trade on Tuesday from their Monday close of $13.33 on the New York Stock Exchange.

(Reporting by Karen Jacobs; Editing by Derek Caney, Dave Zimmerman)