Carlyle Group, which bought Applus+ in 2007 in a deal valuing it at 1.48 billion euros ($2 billion), plans to float the company next year and expects to appoint more banks in the coming months to work as bookrunners, said the person.

Disasters like the 2010 BP Gulf of Mexico oil spill and a growing environmental movement have spurred calls for better health and safety standards in the energy industry, boosting demand for services provided by firms like Applus+.

The Barcelona-based company reported earnings before interest, tax, depreciation, and amortization (EBITDA) of 171 million euros in 2012, up 19 percent on the previous year, helped by acquisitions in what is a fragmented industry.

The share sale, for which Rothschild is acting as an advisor, is most likely to take place in Madrid but a final decision on location will be made on Thursday, the person said.

Details on the flotation, such as the size of the stake to be sold and what it will be valued at, are yet to be decided.

Carlyle and Applus+ declined to comment.

This year has seen a growing number of private equity firms taking advantage of improving stock markets to float their businesses and bankers working on share sales expect this flow of deals to continue in 2014.

Applus+, which has over 18,000 staff across more than 60 countries, has more than doubled its revenues under Carlyle to 1.47 billion euros last year. Around 80 percent of its revenues are generated by clients outside of Spain.

The company has no immediately comparable listed peers as rivals differ in both geographical presence and how much weight they place on their various different activities, but testing and inspection companies SGS, Bureau Veritas and Intertek Group are similar businesses.

Those companies trade on next-12-month EV/EBITDA multiples of 11.5 times, 13 times, and 11.5 times respectively, according to Thomson Reuters data. At a similar multiple and based on 2012 numbers, Applus+ would be worth between 2 billion euros and 2.2 billion euros.

In July, Applus+ hired John Hofmeister, a former Shell Oil president with a long experience of working for public companies, as a non-executive member of its board to help drive Applus+'s expansion in North America and in the services it provides for the oil and gas sector.

($1 = 0.7377 euros)

(Editing by Alexander Smith, Elaine Hardcastle and David Evans)

By Kylie MacLellan and Andrés González