From The Japan Times Online:
In the North Korean nuclear crisis, there is a major difference between having leverage and the ability to use it. China has the former, but not the latter. North Korea has both.
On paper, China has the political, military and economic leverage to effect significant change in the North Korean regime’s behavior and the regime itself. The international community saw glimpses of this leverage when Beijing temporarily shut off an oil pipeline to North Korea in early 2003. At present, however, China is significantly constrained by three factors that North Korea is aware of and uses to its advantage:
