The accumulation of oil by plant seeds is an important physiological and genetic indicator. Despite the fact that the determination of the oil content in seeds by the NMR method is enshrined in international standards (ISO 551, 1984, ISO 10565, 1998), this method is insufficiently applied in physiological and genetic studies. We have made an attempt to increase the informativeness of the NMR-relaxation method in evaluating seed oil content of different cultures.Using the NMR relaxation method, we showed that the maximum oil content (70%) is contained in the nuts of Júglans régia trees: this oil is characterized by the slowest decay of the NMR echoes, i.e. the maximum values of the spin-spin relaxation times T2 (81 ± 2 msec). The oil content (15-25% of the dry weight) in seeds of soybean Glycine max L. is significantly lower, while soybean oil is characterized by a relatively fast attenuation of NMR echo signals (T2 ≈50 msec). Intermediate parameters characterize the seeds of saffron Cárthamus tinctórius (oil content 33 ± 1%, T2 68 ± 3 msec). For comparison, the echo relaxation curves (registration in the time range of 7-63 msec by the Carr-Parcel method, at τ 3.5 msec between 180° - pulses) from protons of pure soybean oils (toluene extract from soybean seeds or refined oils) are characterized by a single exponential curve with T2≈60 msec. When determining the oil content in soybean seeds (Amelina variety, 2017 harvest from the institute field), by the NMR relaxation method it was established that the oil content depended on the seed size. For Amelina variety in samples of different weights (60-80, 100-120, 140-160 and 160-180 mg), the oil content in seeds was 16.0 ± 0.5%, 17.7 ± 0.4%, 19.0 ± 0.3% and19.9 ± 0.1%, respectively. Thus, the oil content increases with seed weight increasing (up to 4-5% of dry weight with an increase in the weight of seeds from 50 to 200 mg). To increase the informational value of the data on the oil content of seeds in physiological and genetic studies, the value of the oil content in the seeds should be accompanied by an indication of the mass of the seeds in which the oil content was determined (for example, oil content 18.7 ± 0.9% in seeds with weight 140 ± 3 mg ) Conclusion. In scientific studies (to increase the informational value of oil content in seeds), the indication of the oil content in the seeds should be accompanied by an indication of the mass of the seeds.