Abstract: A well fluid sampling tool and method for retrieving reservoir fluid samples from deep wells. The sampling tool is lowered to the required depth, an internal sample chamber is opened to admit well fluid at a controlled rate, and the sample chamber is then automatically sealed. The temperature of the sampled well fluid is maintained at or near initial as-sampled temperature to avoid the volumetric shrinkage otherwise induced by temperature reduction, mitigate precipitation of compounds from the sample, and/or maintain the initial single-phase condition of the sample. The sample chamber is thermally insulated, provided with a storage heater, electrically heated, given a high hear capacity, and/or pre-heated to sample temperature.