The effects of rapeseed oil supplements on ruminal digestion and total tract digestibility of nutrients were studied in four cows in midlactation, fitted with ruminal cannulas and used in a Latin square design (three periods x three diets). Treatments were basal diet only (control) or 1 kg of rapeseed oil added to a basal diet by continuous infusion or by a single administration via the ruminal cannula. The ratio of forage: concentrate of the basal diet was 68:32 on a DM basis. Total lipid contents were 3.9, 9.4, and 9.4% of DM in control diets and in diets with continuous and single supplementation, respectively. Fat supply decreased total tract OM digestibility (77.0, 72.0, and 74.0% in control diet and in diets with continuous and single supplementation, respectively) because of a depressive effect on fiber digestion. With both oil administration methods, the relative proportion of propionic acid increased and acetic and butyric acids in ruminal fluid decreased. Moreover, continuous infusion of oil increased the proportion of propionate and decreased the proportion of butyrate. When oil was added as a single administration, ammonia N concentration before feeding was lower than when oil was infused continuously.