Some links suggest oceans account for 70%. (The sites are not consistent as to whether oceans for this purpose include other Seas (eg North Sea, Channel). When lakes and other water are included teh figure increases to 71%
As several have said, about two thirds of the earth's surface is water. However by volume or mass only a small proportion of the earth is water http://water.usgs.gov/edu/earthhowmuch.html (because there is none in the earths core and mantle).