Hierarchical Data Format 5 is a popular file format for storing and managing large amounts of data. It is the format used by NASA for their ACOS and OCO-2 data products, which both contain (among other things) column-averaged CO2 in units of dry-air mole fraction (Xco2). This tutorial demonstrates how to extract the average daily Xco2 value – and total reading count per day – from the HDF5 files into a CSV file for analysis in Excel or Gnumeric.