Oil giant Royal Dutch Shell has overhauled its top-tier legal panel, awarding coveted places to 11 firms for international work.

Slaughter and May remains the FTSE 100 company's principal adviser for corporate mandates across the globe and is joined by UK rivals Allen & Overy, Clifford Chance and Linklaters.

Although other firms were invited to tender in the review, which was finalised last month, the company opted to remain with largely the same list of advisers that it appointed to its panel in its last review in 2004.

Denton Wilde Sapte and Simmons & Simmons were reappointed, while US firms Cravath Swaine & Moore, Debevoise & Plimpton, Vinson & Elkins and Baker & McKenzie also kept their places. Bracewell & Giuliani will continue to cover the company's external legal needs in South America.

Places on the roster are keenly contested. In the past Shell's legal spend has been estimated at more than £50m.

One partner at a panel firm said: "Shell has a huge legal spend and all firms would be pleased to have them on their client roster. It is a very nice panel to be on."

The review was led by Hague-based legal services coordinator Leanne Geale and London legal head Richard Wiseman. Both report to global general counsel Beat Hess in the Netherlands.

This is the Anglo-Dutch company's first panel review since its restructuring in 2005, which saw Netherlands-based Royal Dutch and UK-based Shell combine to form Royal Dutch Shell. Slaughters, De Brauw Blackstone Westbroek and Cravath advised the company on the shake-up, which was one of the UK's biggest-ever transactions.

Shell is the third biggest oil company in the world and last year had global revenues of $318.8bn (£160bn).

Rival oil company BP finalised its first formal review of its advisers at the end of last year. Linklaters, Simmons and Bakers were among the firms appointed to advise on top-level cross-border transactions, and all now operate on both companies' panels.