Regulators have accepted proposals by Wood Group and Amec Foster Wheeler to address competition concerns over their planned £2.2bn merger.
The firms have agreed to sell a range of assets after the Competition Markets Authority (CMA) found the merger could curb competition in the supply of services to the UK oil industry.
The companies were told they could face an in-depth investigation.
Following public consultation, the CMA said the plan addressed its concerns.
Amec Foster Wheeler will now sell off "almost all" assets which contribute to engineering, construction and maintenance services in its upstream offshore oil and gas business in the UK.
Kate Collyer, deputy chief economic adviser at the CMA, said: "It is crucial that competition is maintained in this major UK industry.
"We have therefore conducted a thorough investigation into this merger, and believe that the sale of Amec Foster Wheeler's assets will address our concerns and ensure that customers in the North Sea continue to be able to obtain competitive bids."
She added: "The CMA is committed to conducting merger investigations as quickly and efficiently as possible.
"In this case, the CMA worked with the companies on a 'twin-track' approach, engaging with them on shaping remedies that might mitigate competition concerns, if any were found, whilst still investigating whether such concerns arose.
"This enabled us to promptly reach a final view on the proposed remedy after competition concerns were identified, helping to reduce uncertainty about the potential impact of the merger for customers within this industry."
Robin Watson, chief executive of Wood Group said: "Since we announced the deal in March, both parties have maintained a relentless focus on keeping on schedule.
"Today's earlier than anticipated decision from the CMA allows us to move forward with pace and we are very confident of completing the acquisition of Amec Foster Wheeler in October."
Jon Lewis, chief executive of Amec Foster Wheeler said: "We welcome today's announcement from the CMA.
"We have made significant progress marketing Amec Foster Wheeler's UK upstream oil and gas business to a range of high-quality bidders, which has helped to ensure that we will close the transaction in October, bringing the many benefits of the combined company to our clients, colleagues and shareholders."