The aim of the present study was to evaluate the impact of essential oils (EO) from Lippia turbinata (LT) and Tagetes minuta (TM) as well as the rotation of both EO on fermentation parameters in vitro. Daily addition of LT, TM, or a 3-day rotation between them (TM/LT), as well as a control (without EO), was evaluated using the rumen simulation technique (Rusitec). The experiment lasted 19 days, with a 7-day adaptation period, followed by 12 days of treatment (Days 0-12). The EO were dissolved in ethanol (70% vol/vol) to be added daily to fermenters (300 μL/L) from Day 0. Daily measurements included methane concentration, total gas production, apparent DM disappearance and pH, which started 2 days before the addition of treatments. On Days 0, 4, 8 and 12 apparent crude protein disappearance and neutral detergent fibre disappearance, ammonia and volatile fatty acid concentration and composition were determined. Methane production was significantly inhibited shortly after addition of both EO added individually, and persisted over time with no apparent adaptation to EO addition. The TM/LT treatment showed a similar effect on methane production, suggesting that rotating the EO did not bring further improvements in reduction or persistency compared with the inclusion of the EO individually. Gas production, total volatile fatty acid concentration and composition and apparent crude protein disappearance were not affected by EO addition. Compared with the control, a 5% reduction of apparent DM disappearance and a 15% reduction of neutral detergent fibre disappearance were observed with the addition of EO. Only TM and TM/LT reduced ammonia concentration. Given the significant and persistent antimethanogenic activity of both EO, and the potential of T. minuta to modify nitrogen metabolism, EO from these plant species are of interest for developing new feed additives with potential application in ruminant nutrition that are also likely to be acceptable to consumers.