Occupational Health and Safety is investigating and has said that the incident looks like it was medical and was possibly a heart attack.

The fatality marks the sixth for the company, occurring on or near its sites this year.

A 37-year old contractor died in June after a part fell on his head while he was working on a dozer at the company's Millennium Mine near Fort McMurray.

Instrumentation technician Lorna Weafer was killed the month before in an attack by a black bear.

Contractor Jordan Gahan died along a highway near Suncor's Firebag operation, when his track hoe fell through the ice in March.

Shane Daye, also an instrument technician, died in hospital after a severe injury onsite, while Jerry Cooper, a 40-year-old tailings operator was found dead in a large pool of sand and water in January.

"I want to affirm our ongoing commitment to safety," Suncor president and CEO Steve Williams said in a statement.

"I am deeply saddened by the fatalities in the first half of the year. Our entire organization is engaged in improving our safety performance.

"Safety is our number one value and a critical part of operational excellence."