$ per barrel (million barrels/day)
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
| 1988 | $17.12 | $16.76 | $16.16 | $17.83 | $17.37 | $16.48 | $15.48 | $15.49 | $14.54 | $13.76 | $14.07 | $16.40 |
| 1989 | $17.99 | $17.91 | $19.47 | $21.26 | $20.32 | $20.03 | $19.72 | $18.57 | $19.56 | $20.05 | $19.85 | $21.06 |
| 1990 | $22.86 | $22.07 | $20.37 | $18.39 | $18.21 | $16.69 | $18.52 | $27.29 | $33.85 | $35.95 | $32.46 | $27.34 |
| 1991 | $25.09 | $20.51 | $19.88 | $20.82 | $21.03 | $20.20 | $21.41 | $21.70 | $21.87 | $23.24 | $22.51 | $19.49 |
| 1992 | $18.80 | $18.98 | $18.91 | $20.23 | $20.97 | $22.37 | $21.74 | $21.33 | $21.88 | $21.67 | $20.34 | $19.38 |
| 1993 | $19.01 | $20.02 | $20.30 | $20.26 | $19.92 | $19.06 | $17.86 | $17.98 | $17.34 | $18.14 | $16.66 | $14.51 |
| 1994 | $15.02 | $14.75 | $14.60 | $16.43 | $17.88 | $19.07 | $19.66 | $18.38 | $17.44 | $17.73 | $18.08 | $17.44 |
| 1995 | $18.02 | $18.53 | $18.48 | $19.86 | $19.83 | $18.42 | $17.29 | $18.03 | $18.21 | $17.44 | $18.01 | $19.02 |
| 1996 | $18.80 | $19.09 | $21.34 | $23.51 | $21.24 | $20.35 | $21.37 | $21.93 | $23.91 | $24.90 | $23.72 | $25.41 |
| 1997 | $25.13 | $22.19 | $20.96 | $19.75 | $20.91 | $19.28 | $19.63 | $19.93 | $19.78 | $21.23 | $20.14 | $18.32 |
| 1998 | $16.69 | $16.07 | $15.10 | $15.31 | $14.93 | $13.69 | $14.12 | $13.39 | $14.98 | $14.42 | $12.95 | $11.29 |
| 1999 | $12.48 | $12.00 | $14.66 | $17.34 | $17.74 | $17.90 | $20.08 | $21.27 | $23.88 | $22.67 | $24.89 | $26.08 |
| 2000 | $27.24 | $29.41 | $29.85 | $25.78 | $28.80 | $31.88 | $29.71 | $31.33 | $33.89 | $33.02 | $34.40 | $28.35 |
| 2001 | $29.56 | $29.56 | $27.18 | $27.40 | $28.61 | $27.57 | $26.43 | $27.40 | $26.08 | $21.95 | $19.57 | $19.06 |
| 2002 | $19.41 | $20.49 | $24.34 | $26.26 | $27.06 | $25.49 | $26.92 | $28.34 | $29.71 | $28.85 | $26.29 | $29.45 |
| 2003 | $33.03 | $35.75 | $33.43 | $28.26 | $28.14 | $30.66 | $30.70 | $31.59 | $28.25 | $30.30 | $31.06 | $31.98 |
| 2004 | $34.23 | $34.73 | $36.73 | $36.72 | $40.29 | $38.03 | $40.82 | $44.92 | $45.93 | $53.25 | $48.45 | $43.12 |
| 2005 | $46.82 | $47.96 | $54.17 | $52.96 | $49.85 | $56.39 | $58.67 | $64.96 | $65.54 | $62.42 | $58.28 | $59.42 |
| 2006 | $65.48 | $61.62 | $62.89 | $69.54 | $70.93 | $70.93 | $74.40 | $73.04 | $63.82 | $58.85 | $59.13 | $62.00 |
| 2007 | $54.24 | $59.25 | $60.60 | $63.94 | $63.45 | $67.49 | $74.14 | $72.38 | $79.91 | $85.91 | $94.76 | $91.39 |
| 2008 | $92.98 | $95.38 | $105.47 | $112.62 | $125.37 | $133.93 | $133.38 | $116.64 | $103.94 | $76.61 | $57.29 | $41.44 |
| 2009 | $41.74 | $39.12 | $47.96 | $49.81 | $59.03 | $69.60 | $64.12 | | | | | |