The densification of ceramic compacts of YBa2Cu3O7-x (123) was studied with a vertical dilatometer. The runs effected under isothermal conditions (ISO) covered the 920-970 degrees C range and were performed under static air atmosphere. Also, controlled heating rate (CHR) runs, from about 800 to 1050 degrees C, were conducted at 5 degrees C/min under either flowing oxygen or static air. The ISO data could be satisfactorily fitted by the solution-precipitation (SP) model giving an activation enthalpy of 221 kJ/mol. Furthermore, the CHR data for 920-970 degrees C was also fitted with the same model giving 207 kJ/mol as the activation energy. From analysis of CHR data, the initial stage sintering is driven by solid state sintering between 827-894 degrees C (823-908 degrees C in O-2). Then, in the interval 902-920 degrees C (914-934 degrees C in O-2) the intermediate stage driven by grain growth (GG), competes with the rearrangement process associated to the presence of a liquid phase. This last process applied because the next sintering stage in the range 922-970 degrees C (938-990 degrees C in O-2 flow) could be fitted by the SIP model with an activation enthalpy of 207 kJ/mol (229 kJ/mol in O-2). In the range 972-995 degrees C (990-1014 degrees C in O-2), the solid state (GG) intermediate stage mechanism and/or viscous flow competes with the SP process. (c) 2005 Springer Science + Business Media, Inc.