Could be a crack or hole in the pickup tube. I had that problem in a '84 940GLE.
it is likely your fuel gauge is not working properly
The gas tank on the 2012 Volvo S60 holds 17.8 gal..
The gas tank on the 2006 Volvo C70 holds 15.9 gal..
The gas tank on the 2005 Volvo XC70 holds 18 gal..
The gas tank on the 2008 Volvo C30 holds 15.9 gal..
The gas tank on the 2012 Volvo C70 holds 15.9 gal..
The gas tank on the 2011 Volvo S60 holds 17.8 gal..
The gas tank on the 2011 Volvo S80 holds 18.5 gal..
The gas tank on the 2010 Volvo XC70 holds 18.5 gal..
The gas tank on the 2013 Volvo C70 holds 15.9 gal..
The gas tank on the 2010 Volvo C70 holds 15.9 gal..
The gas tank on the 2009 Volvo C70 holds 16.4 gal..