The four-day biennial event runs until Friday and includes a conference and more than 1,500 exhibitors, including BP, BAE Systems and E-On.
In 2011, the event attracted 48,114 attendees from more than 90 countries.
A new feature this year is The Energy festival, which offers a line-up of live events, music and entertainment showcasing the best of Aberdeen.
From today (3 September) to Thursday, live jazz, international performers and traditional Scottish music will take place in the Quad at Marischal College in Aberdeen's city centre.
A Country Fair will also take place, offering crafts, local produce and street theatre.
There will also be a photography exhibition at Seventeen, Aberdeen’s cultural hub in Belmont Street by charting the impact of the industry on Aberdeen’s growth and development over the last 40 years.