The present invention relates to a process for co-gasification of two or more carbonaceous feedstock, said process comprising combusting a first carbonaceous feedstock having high calorific value with low ash and high hydrogen content, to produce a heated effluent; carrying the heated effluent to second reactor where the heated effluent reacts with a second carbonaceous feedstock, having low calorific value with high ash and low hydrogen content, to produce synthesis gas. The present invention also relates to an apparatus for co-gasification of two or more carbonaceous feedstock, comprising a first reactor (3), having a first feedstock inlet port (1), a oxygen or air inlet port (2), a steam inlet port (9), a ash removal port (7), and a solid recycle port (6); a first cyclone separator (5) connected to the first reactor (3) through a first cyclone separator inlet port (4); a second reactor (16), having a second feedstock inlet port (10), and a ash removal port (15), the second reactor is connected to the first cyclone separator (5) through a gaseous inlet port (8); and a second cyclone separator (12), having a fine particles removal port (13), and an effluent port (14), wherein the second cyclone separator is connected to the second reactor through a second cyclone separator inlet port (11).