I expect Stuart used the annual averages and then quarterly averages.  Nothing wrong with that, just the resolution gets higher to the right hand side of the graph.
I made my own.  Did my own data extract from the first table in the PDF.

http://peakoil.com/post204693.html#204693

Correct - I just took the data right off the Petroleum Review article and plotted each point at the midpoint of the corresponding period (so 7/1 for years, and 2/15 for first quarer etc. It looked too busy with the symbols in so I took them out, or that would be clearer.