contour lines for joint probability distribution

Dear all, I have a question about contour lines. I have two vectors A and B. vector A represents the volumes (m3) and vector B represents discharges (m3/s). I computed a vector C which represents the joint probability distirbution of variables A and B and what I would like to plot is a graph which shows the contour lines for every value of vector C. So for example, one isoline for values of C=0.1, one other isoline for values of C=0.2 and so on. Here an example of what I would like to do. If someone could help me it would be really nice.