Gibson's board of directors unanimously rejected the offer of C$19.94 per share for control of the Calgary-based company, which owns and operates pipelines, oil storage terminals and an oilfield trucking and environmental services division.
On Thursday, the Canada-based Financial Post reported the potential buyer was Singapore-based Asia Pacific Private Equity.
Later in the day, Gibson confirmed in a statement that the offer was made by way of a "non-binding, highly conditional proposal for discussion, from an unknown, unidentifiable foreign entity".
Gibson