Gas sampling in stranded marine mammals can now be performed in situ using the appropriate vacuum tubes, insulin syringes and an aspirometer. Glass vacuum tubes are used for extraction of gas from cavities such as the intestine, pterigoyd air sacs, pneumothorax or subcapsular emphysema as well as for storage of the gas sample at room temperature and pressure. Insulin syringes are used for extraction of bubbles found in veins, then immediately injecting its content into the vacuum tubes for storage. Finally an aspirometer is used to extract and separate the gas mixed with blood inside the heart. We have found that these are reliable tools for in situ gas sampling, storage and transportation without appreciable loss of gas and without compromising the accuracy of the analysis. Gas analysis is conducted by gas chromatography in the laboratory.