A fourty-year period of energy price oscillation

Figure 1. The difference between the headline and core CPI (both seasonally adjusted) since 1957.  The V-shape suggests the similarity of the fall and rise paths. One can estimate the next peak extrapolating the current rise by the previous fall (between 1980 and 2000).

Figure 2. The difference between the headline and core CPI. The red curve is an inverse version of the blue curve reduced by -9 and shifted by 19 years ahead.  One can estimate the distance between the peaks in 1981 and 2019 as the period  of long term oscillations, which is approximately 40 years.  

Figure 3. The difference between the energy and core CPI. The red curve is an inverse version of the blue curve reduced by -65. One can estimate the distance between the peaks as the period  of long term oscillations.  The energy price is likely on a downward trend already.