The Income Tax (I-T) Department is investigating transactions where promoters, their associates and anchor investors bought unlisted stocks of companies and offloaded them during offers for sale (OFS) when the entities went for listing. Over the past 10 days, the department's investigation wing has sent out many notices, questioning such investors in multiple cities on how they computed the 'cost' of acquisition of unlisted shares and the subsequent capital gains on their sale. The tax office suspects several investors pegged the stock purchase cost at an unacceptably high fair market value (FMV) - instead of the actual outgo for acquisition- to lower capital gains and tax numbers, said people in the know.