The Blues are thought to have made Sigurdsson a top target this summer.
Gylfi Sigurdsson celebrates scoring the second goal for Swansea with Leroy Fer
The Blues are expected to be busy this summer as Ronald Koeman looks to spend the funds made available by Farhad Moshiri.
So far they have been quiet in the transfer window though, with Maarten Stekelenburg the only arrival at the club.
Iceland's Gylfi Sigurdsson shoots at goal
That has not stopped them being linked with numerous players in the meantime and Swansea City star Sigurdsson is one of those that has been suggested as a target.
According to the Telegraph, the Blues had made the Iceland star one of their top targets and were willing to bid £25 million for his services.
It was believed that was Swansea’s asking price for their man, but now the Daily Mail reports they have increased their valuation to £30 million.
West Ham's Alex Song and James Tomkins with Swansea's Gylfi Sigurdsson in action
As yet it is unknown whether Koeman would be willing to spend that much on the attacking midfielder.
It would certainly be a big price to pay for him and it remains to be seen if the Dutchman rates him highly enough to pay such a fee to secure his signature.
Everton manager Ronald Koeman before the match against Barnsley