Job management company GeoOp has been sent a please explain letter by the Stock Exchange after a spike in the value of its shares.

Between Christmas Eve and yesterday the company's shares increased more than 72 percent to 64 cents at the close yesterday.

The Stock Exchange wants to know if there's some material information GeoOp should've disclosed to the market.

The company says it's continuing to comply with its continuous disclosure obligation and it's not aware of any specific reason for the price increase.

It says historically GeoOp has been subject to significant volatility as a result of its tightly held share register.