A method of installing a subsea riser for carrying hydrocarbons between a sea bed and a surface, said method being of the type whereby: - a seabed installation is anchored to said sea bed; - a tubular pipe is supplied which has a connecting end intended to be connected to said seabed installation and an opposite end equipped with a submersible float; - water is permitted to enter said float in order to submerge said float and said tubular pipe vertically in line with said seabed installation, while said float and said pipe are held by a suspension line from a surface vessel, said suspension line bearing tensile forces corresponding to the weight of said float and of said pipe; - a pulling cable is supplied and return means are installed on said seabed installation so that said pulling cable can be connected to said connecting end and said cable can be driven through said return means and, at the same time, said connecting end can be driven toward said seabed installation; characterized in that it further comprises the following steps: - a submerged pulling buoy is attached to said pulling cable so as to apply additional tensile forces to said suspension line; - a gaseous fluid is substituted for the water in said float in order to compensate, on the one hand, for the tensile forces corresponding to the weight of said float and of said pipe and, on the other hand, for at least some of the additional tensile forces; and - said pulling buoy is anchored to said seabed installation and said suspension line is gradually released so that said seabed installation takes up said additional tensile forces applied by the pulling buoy whereas said float applies the remainder of the additional tensile forces to said pipe in order to hold it vertically. - a seabed installation is anchored to said sea bed; - a tubular pipe is supplied which has a connecting end intended to be connected to said seabed installation and an opposite end equipped with a submersible float; - water is permitted to enter said float in order to submerge said float and said tubular pipe vertically in line with said seabed installation, while said float and said pipe are held by a suspension line from a surface vessel, said suspension line bearing tensile forces corresponding to the weight of said float and of said pipe; - a pulling cable is supplied and return means are installed on said seabed installation so that said pulling cable can be connected to said connecting end and said cable can be driven through said return means and, at the same time, said connecting end can be driven toward said seabed installation; - a submerged pulling buoy is attached to said pulling cable so as to apply additional tensile forces to said suspension line; - a gaseous fluid is substituted for the water in said float in order to compensate, on the one hand, for the tensile forces corresponding to the weight of said float and of said pipe and, on the other hand, for at least some of the additional tensile forces; and - said pulling buoy is anchored to said seabed installation and said suspension line is gradually released so that said seabed installation takes up said additional tensile forces applied by the pulling buoy whereas said float applies the remainder of the additional tensile forces to said pipe in order to hold it vertically.