The phase diagram of carbon is not experimentally well known at high pressure and/or high temperature. We have determined the phase diagram of carbon by means of Monte Carlo and molecular dynamics simulation methods using the Brenner bond order potential. The melting line of diamond was found to have a positive slope (pressure vs. temperature) with the graphite-diamond-liquid triple point in agreement with an estimated value based on experiment. The present calculation predicts a first-order phase transition in liquid carbon terminated by a critical point and by a triple point on the graphite melting line. The low-density liquid is predominantlyspbonded with littlesp3character. The high-density liquid is mostlysp3bonded with littlespcharacter. ©2000 American Institute of Physics.