The present invention relates to new ether carboxylic acids as high temperature stable rheology modifier, viscosifier, lubricant or emulsifier additives in oilfield and industrial applications. In particular, the invention relates to an ether carboxylic acid or a derivative thereof obtainable by reacting a branched polyol alkoxylate with a halogen carboxylic acid or a halogen carboxylic acid derivative. Further aspects of the invention relate to a lubricant composition comprising an ether carboxylic acid of the invention and the use of said ether carboxylic acid.