Abstract: The present invention relates to plant or vegetable oil-based drilling fluid compositions which are non-polluting and non-toxic, and which provide improved lubricating properties and stability for use under widely-varying load and pressure drilling conditions. The compositions are primarily based on plant or vegetable oils comprising essentially extended long-chain carboxylic acids having minimal double and triple bonds of the 12 to 24 carbon atom series. The oils are selected from the group consisting of peanut oil, rapeseed oil, soybean oil, sunflower oil, corn oil, cottonseed oil, rice bran oil, safflower oil, castor bean oil, palm oil and mixtures thereof. Suitable antioxidants and emulsifiers as well as desired viscosifiers and fillers are included in the compositions which are adapted to addition to water and/or brine for desired rheological properties for drilling fluid uses.