Calgary, Alberta, April 6, 2010 – Nexen Inc. President and CEO, Marvin Romanow, today announced
the appointment of Matt Fox as Executive Vice President, International Oil and Gas. Matt succeeds
Laurence Murphy who retired in late 2009.

Matt joins Nexen after spending 27 years at ConocoPhillips and is a Civil Engineer and holds a Masters
degree in Petroleum Engineering. Prior to joining Nexen, Matt was President and CEO of
ConocoPhillips Canada. He had previously held progressively senior positions in ConocoPhillips
divisions including the Canadian Oil Sands, the United Kingdom, the United States and the Middle East.
Over that period of time he also served as Chief Reservoir Engineer, Conoco Upstream Technology.

“With his extensive expertise in reservoir engineering, Matt will make an immediate contribution to the
advancement of Nexen’s world-class suite of exploration and development opportunities,” stated Mr.
Romanow. “In addition, his experience managing large complex operations in various parts of the world
will make him an important addition to Nexen’s leadership team.”

Nexen Inc. is an independent, Canadian-based global energy company, listed on the Toronto and New
York stock exchanges under the symbol NXY. We are focused on three growth strategies: oil sands and
unconventional gas in Western Canada and conventional exploration and development primarily in the
North Sea, offshore West Africa and deep-water Gulf of Mexico. We add value for shareholders through
successful full-cycle oil and gas exploration and development, and leadership in ethics, integrity,
governance and environmental stewardship.

For further information, please contact:

Pierre Alvarez
VP, Corporate Relations
(403) 699-5202

Lavonne Zdunich, CA
Manager, Investor Relations
(403) 699-5821

801 – 7th Ave SW
Calgary, Alberta, Canada T2P 3P7
www.nexeninc.com