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Chlorophyll climatologies derived from historical in situ data, Coastal Zone Color Scanner data (CZCS) and SeaWiFS (Version 3) data were inter-compared to evaluate their strengths and weaknesses in representing chlorophyll distributions in the global ocean. A fourth dataset, produced by blending in situ data with CZCS data was compared to the other three. Systematic biases were associated with each of these datasets. In situ and CZCS data appeared to underestimate chlorophyll since the blended analysis produced generally elevated values. The underestimate by in situ data is related to problems mostly in the analysis of the data. CZCS underestimates are related to calibration and algorithm problems. The SeaWiFS data for the open ocean appears to be valid since its within 10% of the blended climatology for all seasons except winter. In the coastal ocean, SeaWiFS may overestimate chlorophyll with values 30-77% higher than the next closest climatology. Blending of in situ and satellite may produce the best climatology. This method takes advantage of the higher quality of in situ data, and the spatial variability of satellite sensor data. The blended method may be of greatest use for SeaWiFS in coastal areas, where the algorithm problems are greatest. [ABSTRACT FROM AUTHOR]