Measurements of the heat transfer from a horizontal platinum wire to carbon dioxide over a pressure range from 0·8 to 1·1 of the critical pressure are reported. The heat transfer coefficient at conditions very close to the critical point is very large. Below the critical point in the two-phase region, film boiling appears with uprising vapor in columns or sheets. The sheets are similar in appearance to free convection flows above the critical point. Two similar relations correlate the heat-transfer measurements at bulk conditions both above and below the critical point.