By Jeffrey Dastin

(Reuters) - United Continental Holdings Inc <UAL.N> is reviewing its management structure and how it routes flights through various hubs in an effort to operate more efficiently and cut costs, Chief Executive Officer Oscar Munoz said in an employee letter that Reuters saw on Wednesday.

The review is part of an ongoing attempt by United and its reshuffled board to cancel fewer flights, win customers and narrow a profit margin gap with rival Delta Air Lines Inc <DAL.N>.

Separately, United said in a filing on Wednesday that it expected to cut flight capacity from its Houston hub between 1 percent and 2 percent in 2016 while increasing its emphasis on San Francisco and Denver.

A decline in oil prices over the past two years has prompted United's energy-industry clients to cut back on travel spending. The No.3 U.S. airline by passenger traffic also expects corporate customers generally to book lower fares in the second half of 2016, Chief Revenue Officer Jim Compton said on a call with analysts on Wednesday.

Analysts have called on United to fly less from Houston and more from other airports, but the company has said it would not have major changes to announce until the winter.

United shares were up 2.5 percent at $49.06 in afternoon trading, buoyed in part by a $2 billion buyback and higher-than-expected earnings announced after Tuesday's market close.

(Reporting by Jeffrey Dastin in San Francisco; Editing by Chizu Nomiyama and Lisa Von Ahn)