Where was the data
Energy relevant data sets are from US Energy Information Administration.
The data is available from http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm.
I spent some time searching for population data of whole world on Internet before I found that EIA has a population data in the same page as Energy data!
How did I get the data
At first, I didn't know that the default data is from 2005 - 2009 (or 2006 - 2010 for some newly updated data set). After I found this, I updated the display to 1980 through 2009 and downloaded all 7 data sets as Excel files.
What did I do to the data
I found that directly copy all data into a plain text file won't work. I also failed several time using different ways (such as changing extension of files to .txt or .tsv) before I finally found that the error in my first try was due to the wrong TABs in .txt files.
After I deleted unnecessary TABs, my app could parse the data correctly!
Next step was to change 'NA' (for data not applicable) and '--' (for data of countries that not there in that year) to some significance number (here I used -10 and -1) for future use. But I never had a chance to use them (because of the existence of FloatTable class provided by Ben Fry, author of Visualizing Data) since then.