Fat inclusion can increase energy density of diets fed to ruminants, but detrimental effects to nutrient digestion have been reported. There is evidence that not all fat sources have this negative response and this effect can vary depending on the forage concentration in the diet. The objective of this experiment was to determine the effects of including different types of unsaturated fats to high and low forage diets in vitro digestibility and fermentation. An experiment was conducted using an in vitro gas production (GP) system. Treatments included either low forage (LF; 35%) or high forage (HF; 70%) with 2 dietary fat concentrations (6 or 9%) and of 7 different fat source treatments (control + 6 different types of unsaturated fat sources). The control diet had a basal level of fat in the diet [3% fat (0% fat inclusion); and fat sources were added to attain 6% or 9% fat and consisted of (Coconut oil, CO; Poultry fat, PF; Palm oil, PO; Palm kernel oil, PKO; Ca Salts, MEG; Soybean oil, SOY)]. Modules (GP) were randomly assigned to treatments in a 2 × 2 × 7 factorial design and incubated for 2 24 h runs. A randomized complete block design with 4 replicates per treatment and 2 runs was used. Run was the blocking factor. Data were analyzed using the MIXED procedure of SAS. Apparent digestibility (AD) for DM, OM, NDF, ADF and true dry matter digestibility (TDMD) were higher in LF-treatment. Cumulative gas produced in mL was greater in LF (P = 0.01). Fat concentration had no effect on AD, but the 6% fat had a higher gas production (P = 0.03; 109.6 vs. 103.5 mL ± 2.44). The CO had the highest DM AD followed by SOY and PF (54.5, 51.8, and 50.6% ± 0.48) and cumulative gas production followed same pattern. The TDMD and OM AD were higher in CO; however, the NDF and ADF AD were higher in MEG-fed modules. Final pH was not affected by treatments. Final NH₃N concentration was greater in HF and 9% fat. These results suggest that LF diets with high dietary fat concentration can be utilized and different types of fat sources may improve DM and fiber rumen digestibility.