African oil major Tullow Oil is under pressure to part with its CEO Aidan Heavey. Despite Heavey’s entrepreneurial skills transforming the Irish oil finder into one of the most successful explorers in the world, he has clearly become a victim of his own success. Doubts have started to materialise over whether he can turn the company from an oilfield explorer to an oilfield developer.

Heavey’s founded Tullow Oil in 1986 as a former accountant and more than 25 years later, the firm has a market value of £10.7 billion, making it the fourth biggest oil firm to be listed on the London Stock Exchange and putting it on par with giants like BP, Shell and BG Group.

But like BG Group experienced with the 12 year tenure of its CEO Frank Chapman, a long reign does not guarantee safety from the inevitable perils of business; Chapman was replaced in early 2013 after the firm was hit with production problems, cost overruns and a depreciating market value.

In Tullow’s case, the vast oil reserves the company has found in Ghana and Uganda could provide a saving grace – however finding the oilfields is a different ballgame to setting up a viable and efficient production line.

Tullow shares are beginning to plummet. Since last year, the share price has fallen from £16 to a £11.83 at the end of January 2013. The broker Investec has promptly rated the company a “sell” and has put the target price at just £10.

The main reason for the drop in share prices is the company’s failure to meet production targets at its Jubilee oilfield off the coast of Ghana due to “operational hiccups”. Next to these oilfields, Tullow also found a highly lucrative set of oil fields, known collectively as the TEN. Despite the find, the size of the oilfields may prove to be Tullow’s downfall; the projected development cost of the TEN is at an estimated £3.2 billion, a sum deemed too large even for a firm of Tullow’s stature. Reports from the company suggest that it will reduce its share in the project as a result.

The problems continue elsewhere; in Uganda, the firm is locked in two separate arbitration cases; one relating to the recovery of $404 million capital gains tax arising from its $1.45 billion acquisition of Heritage Oil’s Uganda assets, and the other concerning a lawsuit the firm has brought against the Ugandan government for placing VAT on goods and services it purchased during its operational work in the country.

Tullow Oil is also at odds with the Ugandan government over a $1.5 billion refinery plant it has agreed to build. The government are now demanding that the company builds it nine times bigger and has announced the project will be put on hold until the deadlock can be broken. The scale of the government’s demands would bring the project’s costs up considerably for Tullow.

The scale of these projects worries investors, but despite this Heavey sought to quell these concerns by pledging to drill an astounding 40 exploration well in 2013, nearly double the amount BP will drill.

Tullow is clearly managing more projects than ever and the question remains as to whether Heavey will be able to handle the pressure if and when more troubles are landed at his doorstep.