Electrochemical reduction of CO2 under high pressure on a glassy carbon (GC) electrode was investigated. The selectivity of the reduction products depended strongly on the current density. CO2 was reduced to CO with a faradaic efficiency of 44% and to formic acid (30%) at a constant current density of 50 mA cm(-2) under 30 atm of CO2 in 0.1 mol dm(-1) KHCO3 aqueous electrolyte. The faradaic efficiency for CO2 reduction decreased drastically with increasing current density. In addition, formation of hydrocarbons such as methane, ethane, propane, and butane was observed. C3 and C4 hydrocarbons such as propane and n-butane were preferentially produced in the electrolysis at small current densities.