Yes, 5%, 10%, even 20%. It all depends on the strain and how it's grown. A strain like Northern Lights, White Widow, or Jack Herer, that is allowed to fully mature without seeds can have THC concentrations up to 20%. Something like that will be pretty pricey, $300+ an oz, but is worth it. From what I have read 20% is about the upper limit right now but who knows what they'll be growing in a few years.