The oxidative dehydrogenation (ODH) of n-butane, butenes and butadiene over VMgO catalyst containing 30 wt.% V2O5 was investigated. Reactivity of hydrocarbons in ODH decreases in the order 2-butenes > 1-butene > n-butane much greater than butadiene. Butenes are easily converted, exhibiting a 64% selectivity to butadiene while a small part 5% is isomerized. The intermediate products (butenes, butadiene and carbon monoxide) were added to the feed in order to get information on the relative importance of primary and secondary reactions. Analysis of the experimental results, derived from adding of intermediate products, led to the proposal of a reaction network comprising of 10 consecutive and parallel steps and the calculation of the reaction rate of each step. The catalyst showed significant activity in the absence gas phase oxygen, indicating the participation of lattice oxygen in the ODH of n-butane.