The deal, understood to be worth nearly £10 million, gives Aberdeen-headquartered OEG access to a stream of new products and clients, in addition to new geographical bases.
OSCA, owned by managing director Bob Smith, provides containers and associated equipment to the energy sector, as well as environmental services such as waste transport and haulage.
In addition to OSCA'S 2500-unit stock, the deal gives OEG bases in Azerbaijan, Kazakhstan and Turkmenistan.
It also gives it stocking locations in Sakhalin, the island off Russia's far eastern coast, and the African nations of Gabon, Congo and Angola.
OSCA'S 35 staff will transfer over to OEG, taking the Aberdeen firm's headcount to 165, and its brand will continue to be used as a division of the OEG Group. It will be led by long-standing commercial manager Donald Guthrie, who has been promoted to regional director and described as the "ideal candidate" for the role.
Mr Smith, who was the majority shareholder in OSCA, will remain with the business..
He said: "After establishing the business in 1996, we have had tremendous success and recently worked in parallel with OEG.
"I have no doubt OSCA will secure further growth as part of the group.
"Achieving international certification and setting new standards for the quality and reliability of container and cargo equipment has been a core focus for OSCA, principles which are also the foundation of OEG's business."
OEG, which now has bases in areas it previously served with distributors, sells and rents equipment from its 13,000-strong stockholding to clients in more than 20 countries.
The company, which offers a design and manufacturing service, has cargo carrying units and engineering cabins in locations around Europe, the Americas, Middle East, Asia Pacific, Australia and the Caspian Sea.
In its most recently available accounts available at Companies House, OEG Group booked a pre-tax loss of £855,713 for the period August 1, 2011 to August 31, 2012. It recorded a £1.8m profit the year before.
Turnover rose to £19.6 million from £9.84 million.
John Heiton, chief executive of OEG Offshore, said: "OSCA is a perfect fit for us, as the largest specialist provider of containers and cuttings cargo storage in the Caspian region as well as to Sakhalin and West Africa, it links seamlessly with our successful North Sea, African, Asian Pacific, Australian and Americas' operations.
"The business has been hugely successful for more than 18 years, delivering European standard and DNV-certified container and cargo solutions to operators and the supply chain.
"Its products and experienced team are a huge asset for OEG.
"As part of OEG Group, OSCA'S market-leading position in the Caspian provides existing clients with new products from stock, and introduces our wider offering to a range of new clients."