Prime Markets recommends to buy shares of budget airline easyJet, saying that today's first-half guidance upgrade provides 'great upside momentum'.easyJet this morning that its financial performance in the first half of the year would exceed guidance it gave in January. The company said improvements in revenue management combined with marketing and website initiatives had enabled it to take advantage of weaker competitors leaving the market. As a result, the board expects a pre-tax loss for the six months to the end of March of between £110m and £120m compared with the previous expectation of a pre-tax loss of £140m to £160m. "Prime Markets have long viewed Easyjet as the great British success story of the airline industry, with a business model that is both relevant and scalable for the global economic environment today and in the future," said head of dealing Richard Curr."Today easyJet have exceeded expectations for H1, and the fact this has come in spite of a huge hike in the fuel bill shows just how powerful a force for growth the low cost carrier has become," he said.The broker believes that an upgrade for second half numbers could be on the cards. For now, they remain unchanged.It says that the shares should comfortably hit and exceed new 52-week highs at or above the 500p 'benchmark' last seen in Spring 2010.BC