Other posts and discussion have left at least one thing clear. That is that only Carbon-Oxygen white dwarf stars will become Type Ia supernovae if enough mass is accreted to exceed MChandra, about 1.39 solar masses. Others can use the more common 1.44 Msolar since it isn't important to detail here. But, the composition of any white dwarf will depend on the mass (and some other factors) of the progenitor star. (The bolded highlights in the following were inserted by Labguy to emphasize certain phrases) http://188.8.131.52/search?q=cache...e+dwarf"&hl=en&gl=us&ct=clnk&cd=49&lr=lang_en And:http://www.geocities.com/tonylance/dwarf.html So, for the many white dwarfs that formed from the far more numerous small stars there must be a large number of He white dwarfs. And the larger stars also do not form not carbon-oxygen rich dwarfs. Therefore: and: http://chandra.harvard.edu/chronicle/0400/sirius.html And: http://online.itp.ucsb.edu/online/gravity_c03/lindblom/pdf/Lindblom.pdf Therefore, from the handy links and quotes provided I would conclude that: (1) Since smaller stars are far more numerous in the universe than large stars, more white dwarf stars are formed with an He composition. (2) The largest white dwarf progenitors also do not lead to a carbon-oxygen composition. (3) Regardless of mass accreted, most white dwarfs will not result in a Type Ia supernova even if MChandra is exceeded. (4) For all white dwarf stars existing, the required C-O composition needed for a Type Ia supernova could be considered "rare" regardless of accreted mass. I am very interested in this and related stellar evolution subjects, so if any of this seems unclear or invalid please provide me with a link or two for consideration.