No, they are not write once disks. All my CDs and DVDs are either -RW or +RW. I mainly use them like a floppy, writing and rewriting over again. But as soon as I start they show as having zero space available. The pie chart shows them as fully recorded, even with just a small tect file or single jpg. So I cant tell how much space is left. This applies whether I use WXP burner or the NTI burner / File CD.