This paper presents the synchronisation of economic cycles of GDP and crude oil and oil
products cargo volumes in major Polish seaports. On the one hand, this issue fits into the concept
of sustainable development including decoupling; on the other hand, the synchronisation may be
an early warning tool. Crude oil and oil products cargo volumes are a specific barometer that
predicts the next economic cycle, especially as they are primary sources of energy production. The
research study applies a number of TRAMO/SEATS methods, the Hodrick–Prescott filter, spectral
analysis, correlation and cross-correlation function. Noteworthy is the modern approach of using
synchronisation of economic cycles as a tool, which was described in the paper. According to the
study results, the cyclical components of the cargo traffic and GDP were affected by the leakage of
other short-term cycles. However, based on the cross-correlation, it was proved that changes in crude
oil and oil products cargo volumes preceded changes in GDP by 1–3 quarters, which may be valuable
information for decision-makers and economic development planners.