Gas price hysteresis, Spain 2015

We begin the new year redoing our hysteresis analysis for Spanish gas prices with data from 2015, obtained from the usual sources:

• Retail gasoline and gasoil prices from the European Commision Oil Bulletin.
• Brent oil spot prices from the the US Energy Information Administration.
• Euro to dollar exchange rates from FXHistory.

The figure shows the weekly evolution during 2015 of prices of Brent oil and average retail prices without taxes of 95 octane gas and gasoil in Spain, all in c€ per liter.

For gasoline, the corresponding scatter plot of Δ(gasoline price before taxes) against Δ(Brent price) is

with linear regressions for the entire graph and both semiplanes Δ(Brent price) ≥ 0 and ≤ 0, given by

overall → y = f(x) = b + mx = −0.1210 + 0.2554x,
ΔBrent ≥ 0 → y = f₊(x) = b₊ + m₊x = 0.2866 − 0.0824x,
ΔBrent ≤ 0 → y = f₋(x) = b₋ + m₋x = 0.3552 + 0.4040x.

Due to the outlier in the right lower corner (with date August 31), positive variations in oil price don't translate, in average, as positive increments in the price of gasoline. The most worrisome aspect is the fact that b₊ and are b₋ positive, which suggests an underlying trend to increase prices when oil is stable.

For gasoil we have

with regressions

overall → y = f(x) = b + mx = −0.0672 + 0.3538x,
ΔBrent ≥ 0 → y = f₊(x) = b₊ + m₊x = −0.2457 + 0.2013x,
ΔBrent ≤ 0 → y = f₋(x) = b₋ + m₋x = 0.2468 + 0.3956x.

Again, no "rocket and feather" effect here (in fact,  m₊ is slightly smaller than m₋). Variations around ΔBrent = 0 are fairly symmetrical and, seemingly, fair.