Based in Aberdeen, Scotland, OEG provides equipment to the offshore oil and gas industry.
Operating in more than 25 countries with more than 160 employees, OEG has modular buildings that can be used as temporary office space or laboratories to carry out work on offshore platforms or rigs.
The firms did not disclose the financial terms of the transaction and the executive management of OEG will retain a stake in the business.
OEG CEO John Heiton said: "We have achieved significant growth in OEG to date but our teams have the appetite to accelerate our further development through both organic and acquisitive means.
"We believe that KKR will be an excellent partner to achieve those aims, given their global network and experience as a leading investor in the energy services sector."
KKR member and head of UK operations Dominic Murphy and KKR Europe director and head of energy Josselin de Roquemaurel said, "OEG has built an impressive track record of growth and has an exciting development path ahead, expanding its fleet, geographic coverage and suite of products and services."
