Petroleum Economics is a very specific area of study, and therefor there don't seem to be any universities in Canada offering a Masters in that exact subject, however there are some courses that are very similar.
Also, with masters programs, you are usually required to complete a thesis, which you can choose the topic of, so you could elect to concentrate on Petroleum economics here.
It looks as though the University of Calgary is the best option, course wise. They offer a masters degree in Chemical and Petroleum Engineering which you can take as a MSc, or MEng (either course or thesis based).
The University of Alberta offer a Master of Engineering and Master of Science program in their Graduate studies, and list Petroleum Engineering in the research area for civil and environmental engineering, but you may need to contact them directly to find out exactly what options are available to you in this field.
