The Calgary-based company had $647 million of net income, or 76 cents per share in the third quarter.
That's down from $1.04 billion or $1.22 a year earlier and below the estimate of 98 cents per share.
Imperial's revenue was $8.6 billion, up from $8.3 billion a year earlier, but less than the estimate of $9.5 billion.
The company says its third-quarter profit fell because of lower margins at its refinery operations — part of an industrywide decline.
Imperial's net income from downstream operations, which include refining, distribution and retailing, dropped to $46 million from $490 million in the third quarter of 2012.
Its upstream operations, which include Imperial's oilsands, offshore and conventional production, had $604 million of net income — up $106 million from a year earlier.