O'Neil was elected Secretary-General of the IMO from 1990 for the first term of office, from 1994 for the second term, from 1998 for the third term, and from 2002 to 31 December 2003 for a further two-year term. He was the second longest serving IMO General Secretary.

Kitack Lim, the current IMO Secretary-General, expressed his sincere condolences to the Canadian Government, to the remaining family of O'Neil, and to the condolences of the entire membership and staff of the IMO.

“It is with great sadness that we have learned of the passing of Mr. O’Neil, who was a great friend and mentor who made a huge personal contribution to securing globally applicable safety, security and environmental standards,” Kitack Lim stated.

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