This weekend Aidan Heavey will represent Ireland at the Ernst & Young World Entrepreneur of the Year awards in Monte Carlo. He will be among 32 entrepreneurs from all corners of the world hoping to walk away with this prestigious title.

His presence at this event testifies to his achievement in building the €3.4 billion oil and exploration company Tullow Oil into one of the largest independent European firms in its sector.

Heavey says that while he was a reluctant participant in the Entrepreneur of the Year programme, it has been an enjoyable and valuable experience and, above all, it has refreshed his memory about how hard it was to get into the oil business. "Things are a lot easier now. It has left me wondering: are we being too complacent?" he says.

Heavey is an unlikely oil baron. His first encounter with Tullow Oil was during a brief stint when he worked as a financial controller for Tullow Engineering, a company owned by the Nolan family that included the Tullow Oil subsidiary.

A conversation with a banker in the mid-1980s highlighted an opportunity to get into the oil business. "He mentioned that there were a lot of small oil fields that had been left behind by the big oil companies," he says. "I decided to grasp it and that led us to get started in Senegal. Twenty years ago oil was the business to be in. It was an exciting time. It was akin to the dotcom era."

A young bean counter running a fledgling oil company was a rare phenomenon in 1985 and it was hard to get the banks and the industry technicians to take him and Tullow Oil seriously, says Heavey.

"The banks wouldn't lend us any money. I had no oilfield experience and it was hard to find technical people to work for someone who knew nothing about the business." He hired consultants who he found in the Golden Pages to get the projects up and running and took it from there.

Tullow Oil got its first exploration licence in Senegal in 1988. That year was its toughest. "It was a long negotiation. I paid the staff salaries myself from borrowings and other resources for the first year and a half."

Heavey says he doesn't remember ever really weighing up the risks of getting into a business that requires the deepest pockets. "I never dreamt for one minute that I wouldn't get the company up and running. I never felt that I was taking a risk," he says. "I don't think entrepreneurs think about that."

Tullow had acquired a few key shareholders by this stage but the company only became self-sustaining in 1990. "You have to spend huge money. A well could cost you up to $20 million (€15.5 million) and even when you make a profit the cashflow may not be sufficient to sustain the company," he explains.

The company often had to do some unusual deals to survive. "In Yemen we did a deal one weekend and sold it two weeks later and made $7.5 million. That kept us going for 12 months," he recalls. "We had to be inventive to raise money."

And going up against oil giants such as Shell and Exxon Mobil wasn't easy. "In the early days major oil companies threatened to put me out of business if I didn't back off on licences. We made mistakes in the past. We took on some big companies head on. That was our own arrogance. Now we work with them rather than against them," he explains.

While Tullow began exploration in Africa, it became active in south Asia in 1990 and in the UK gas market in 2001. The company is quoted on the London and Irish stock exchanges and has 90 licences across 15 countries in northwest Europe, Africa and south Asia. It expects production to grow to more than 80,000 barrels of oil equivalent a day during 2007 and has reserves of more than 358 million barrels of oil equivalent.

With oil and gas prices soaring, Tullow's shares are trading at all-time highs and its website boasts that the company has delivered a 325 per cent return to its shareholders over the past five years. Heavey's own stake in the company is worth almost €30 million.

Today he is the longest-serving chief executive in the industry, steering the company for 20 years. He remarks that Tullow is also the only independent oil company of that era that has survived in Ireland and Britain. "That is probably the greatest kick for me - that Tullow went from being a joke to being the only one," he says.

He puts the company's current success down to the groundwork that was prepared over the past couple of years.

Heavey firmly believes that businesses that take the long-term view tend to be the most successful. "Family businesses, for instance, tend to build a strong foundation and keep preparing for the next generation. Tullow isn't a family business but it is a long-term business, which means that we can go on through the peaks and troughs," he says.

"When I leave Tullow I will be happy to pass it on to someone else and go and play golf," he says. "It's a long-term business. I will make sure it will be there for the long term and that there is a whole generation of people who can take over the reins."