The Carlyle Group and Onex Complete Acquisition of Allison Transmission from General Motors

Market Wire, August, 2007

All amounts in US dollars unless otherwise stated

Onex Corporation (TSX: OCX) and The Carlyle Group announced today they have completed their $5.575 billion acquisition of Allison Transmission from General Motors Corporation. The transaction was first announced on June 28, 2007.

Allison Transmission designs, manufactures and markets automatic transmissions and Hybrid propulsion systems for on-highway trucks and buses, off-highway vehicles and equipment and military vehicles worldwide. The company, headquartered in Speedway, Indiana, employs 3,400 people and sells its transmissions through a worldwide distribution network and sales offices in North America, South America, Europe, Africa and Asia. Allison Transmission generates annual revenues in excess of $2 billion.

Allison's Chief Executive Officer, Larry Dewey commented, "We're excited about our future with Carlyle and Onex, which includes plans for new products, new markets, and global growth across the breadth of our business sectors."

The equity investment of approximately $1.5 billion is split equally between Onex and The Carlyle Group. Onex' share of the investment will be made by Onex Partners II LP and Onex Corporation itself. Carlyle's share of the investment will come from Carlyle Partners IV, its flagship U.S. buyout fund.

About Onex

Onex makes private equity investments through the Onex Partners and the ONCAP family of funds. Onex also has a real estate fund and a public market fund. Through these activities, Onex generates annual management fee income from third-party capital and is also entitled to a carried interest on CDN$4.7 billion of that capital. In addition Onex invests its own CDN$5 billion of capital in both direct investments and as a Limited Partner in its funds. Onex' operating companies generate annual revenues of CDN$33 billion, have assets of CDN$37 billion and employ 227,000 people worldwide. Onex shares trade on the Toronto Stock Exchange under the stock symbol OCX. For more information on Onex, visit its website at www.onex.com . The company's security filings can also be accessed at www.sedar.com .

About The Carlyle Group

The Carlyle Group is a global private equity firm with $71.4 billion under management. Carlyle invests in buyouts, venture & growth capital, real estate and leveraged finance in Asia, Europe and North America, focusing on aerospace & defense, automotive & transportation, consumer & retail, energy & power, healthcare, industrial, infrastructure, technology & business services and telecommunications & media. Since 1987, the firm has invested $28.3 billion of equity in 636 transactions for a total purchase price of $132.0 billion. The Carlyle Group employs more than 800 people in 19 countries. In the aggregate, Carlyle portfolio companies have more than $87 billion in revenue and employ more than 286,000 people around the world. www.carlyle.com .

This news release may contain forward-looking statements that are based on management's current expectations and are subject to known and unknown uncertainties and risks, which could cause actual results to differ materially from those contemplated or implied by such forward-looking statements. Onex is under no obligation to update any forward-looking statements contained herein should material facts change due to new information, future events or otherwise.

Contacts: Onex Corporation Seth Mersky (416) 362-7711 Website: www.onex.com The Carlyle Group Chris Ullman (202) 729-5399 Website: www.carlyle.com