Royal Dutch Shell Plc
Tullow said on Wednesday the planned partnership would focus on making transformational discoveries in underexplored frontier basins.
Nonetheless, weaker than expected production guidance of between 78,000 and 86,000 barrels of oil equivalent per day (boepd) for 2012 pushed Tullow shares 7.1 percent lower to 1,352 pence at 0848 GMT.
Analysts at Bank of America Merrill Lynch said analysts' consensus had been for output of 91,000 boepd, while Citigroup said it had forecast 96,000.
London-based BP Plc
The collapse of oil prices to $10 barrel in the 1990s killed the appetite of industry leaders like Shell and Exxon Mobil Corp
Consequently, in the past decade and a half, independent explorers have led the way in opening up new multibillion-barrel oil provinces in Africa and South America.
The oil majors also came late to the shale gas revolution in the United States and were forced to pay big prices for the first movers -- Exxon last year for instance bought Phillips Resources and related company TWP for $1.7 billion (1.1 billion pounds), picking up about 317,000 acres for exploration in the Marcellus shale basin.
Yet some analysts doubt the majors can quickly turn around their reliance on acquisitions of oil fields or smaller producers to replace the oil and gas they pump each year.
Shell's plan to tie up with Tullow could provide a short cut to its effort to boost discoveries, by tapping into Tullow's expertise and a culture that encourages exploration risk-taking.
Equally some governments still prefer to have very large oil companies exploring for or developing their resources.
Tullow Chief Operating Officer Paul McDade told Reuters in a telephone interview that partnering with Shell could help Tullow gain access to projects it might otherwise not be chosen for.
The new venture will build on Shell's entry into Tullow's exploration licence in French Guiana in 2009, where the partners announced a significant discovery last year.
Tullow has grown from an industry minnow in the 1990s into Europe's largest independent oil explorer, with a market value of over $20 billion, on the back of major discoveries in Uganda and Ghana.
It is also exploring in Ethiopia and plans to drill a well in Kenya, areas which analysts say could emerge as important oil and gas producers.
(Editing by Hans-Juergen Peters and David Holmes)