LONDON (Reuters) - Compass Group (>> Compass Group plc), the world's biggest catering company, launched a 500 million pound ($809 million) share buyback on Wednesday, its third in as many years.

The British firm, which employs more than 500,000 people to feed office workers, soldiers and school children, also reported underlying pretax profit up 9 percent to 1.2 billion pounds in the year to end-Sept, slightly ahead of analyst expectations.

New contract wins in the U.S. and emerging markets, particularly its deals with Ascension Health and Texas A&M University , pushed organic revenue growth to 4.3 percent. Revenue for 2013 was 17.6 billion pounds.

Compass, which estimates that the outsourced food market is worth around 200 billion pounds, also signed new deals with LinkedIn (>> LinkedIn Corp), the Massachusetts Institute of Technology and AEGON USA (>> AEGON) this year.

The firm reported its highest ever operating margin of 7.1 percent, helped by it closing businesses and exiting uncertain contracts in Europe. It said conditions in Europe and Japan, where it gets just over a third of its revenue, would remain tough.

Its biggest rival Sodexo (>> SODEXO) warned earlier this month that austerity-hit Europe and a slowdown in emerging markets would weigh on its results in the short term.

Compass also increased its dividend by 12.7 percent on a year earlier to 24 pence.

(Reporting By Christine Murray, Edited by Paul Sandle)

Stocks treated in this article : SODEXO, AEGON, LinkedIn Corp, Compass Group plc