I must have been lucky cause I used the juice cartridge with THC Oil and had no problems at all. Perhaps I was just lucky, but I burned a whole gram of oil and had no leakage problems and it burned very well. One must take into consideration that different folks will make their oil differently, so perhaps my was perfect. Who knows the next oil I put in it may not burn well at all. The only hassle for me was the process of boiling water and putting the oil syringe into it to thin out the oil so I could inject it into the top of the oil cartridge. Also, I didn't fill the cartridge all the way to the top.