Abstract: An organopolysiloxane composition capable of cure to an elastomeric body, the composition Comprising an organopolysiloxane containing polymer having not less than two reactable silicon-bonded groups selected from alkenyl group, condensable groups, silyl-hydride groups and/or one or more trialkylsilyl containing terminal groups, optionally a siloxane and/or silane cross-linker having at least two groups per molecule which are reactable with the reactable groups in (a); 5 to 50% by weight of the composition of at least one compatible natural oil and/or natural oil derivative based extender and/or plasticiser; a suitable cure catalyst and optionally one or more fillers. The compositions are particularly useful as sealants.