Controlled release of additives in fluid systems

A container for releasing a chemical additive in a fluid material selected from a lubricant or hydraulic fluid composition comprises a fluid material-impermeable casing having a hollow interior and an additive composition comprising at least one fluid material-soluble additive. The additive is held within the container by a least one fluid material-permeable element provided at or near an opening in the casing and is effective to provide for release of additive(s) into the fluid material. Methods of releasing additives into fluid material are also provided.