Crop-weed competition and interactions are the focus of many researchers to make weed management decision accurate and economical. Therefore pot and field studies were conducted in two consecutive years (2012-13 and 2013-14) at two different locations viz Peshawar (34.0167° N, 71.5833° E) and Chitral (35° 50'' 46 N, 71° 47'' 9 E) of Khyber Pakhtunkhwa (KPK) province, Pakistan. The aims of the experiments were to determine the competitive ability of wild oat (Avena fatua L.) with wheat (Triticum aestivum L) at two ecologically different locations and the possible effects on quantity and quality of wheat grains. In field studies, the experiment was laid out in randomized complete block design (additive design) with three replications in which the seed rate of wheat (var. Ata-Habib) was 125 kg ha-1 while wild oat was sown at 0, 5, 10, 15, 20, 25, 30, 35, and 40 plants m-2. All other weeds were removed manually. Field data showed that number of spikes m-2, number of grains spike-1, and biological yield of wheat during year 1 and plant height and spike length of wheat during year 2 were significantly higher at Peshawar when compared with Chitral. However, the grain yield of wheat was statistically similar at both the locations. The effects of different wild oat densities during both the years were prominent by significantly decreasing the grain and biological yield related variables of wheat. During both the years, the number of tillers and spikes in wild oat-free plots were significantly higher than wild oat infested plots; depending on density. Wild oat density above 5 m-2 resulted in decreasing the wheat yield components. These results showed that wild oat start competition at initial stage of the wheat. All other yield related variables of wheat were decreased with the increasing density of wild oat, indicated that wild oat compete with wheat throughout the crop season. The grain yield losses in wheat ranged from 2-35% during year 1 and 1-21% during year 2 at wild oat density of 5-40 plants m-2. The interaction of location and treatments on biological and grain yield was significant; showing that certain environmental factors favoured the wheat. Like wheat, wild oat biomass and plant height was also higher at Peshawar as compared to Chitral. The quality variables of wheat grains showed that protein content in wheat grains was decreased at higher densities of wild oat. During year 2, the gluten content in Chitral was decreased with increase in density of wild oat. The replacement series experiment showed that the relative yield total (RYT) was vi close to 1; indicating that both species are equally competitive although wheat was relatively dominant species (under field conditions) in mixtures. The same experiments (additive and replacement series) were conducted in pots. The density of wheat was kept constant (10 plants pot-1) while the densities of A. fatua were 0, 1, 2, 3, 4, 5, 6, 7 and 8 plants pot-1. Biomass of wheat and wild oat (pot-1) were recorded. While in replacement series experiment, the same protocol was used except, that there were eleven treatments and the total density of crop and weed (wheat and wild oat) in each pot was constant, but species grown together were varied from 0 to 100%. Plants established in a mixture with proportions of 10:00, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9 and 0:10 (wheat : wild oat) plants pot-1. Pot experiments showed that wheat biomass was similar during both years while wild oat biomass was significantly higher. Wheat and wild oat biomass was decreased (R2 value of 96 %) for wheat and wild oat (R2 value of 94 %) in quadratic fashion. Relative yield total (RYT) showed that both the species are competitive where wheat was dominant in term of biomass production under the mentioned cultural practices. The regression equation demonstrated a good fit to the data with R2 values of 89% in year 1 as compared 96% during year 2. However, wild oat gave higher RYT in pots as compared to field conditions. In light of the present studies, it is concluded that presence of wild oat decreased all yield and biological yield related variables of wheat. Because early stage and later stage related variables of wheat were decreased, suggested that wild oat competes with wheat throughout the crop season. Apart from these, the quality variables of wheat; especially protein content is decreased due to presence of wild oat at higher density. Hence management of wild oat at any location needs to be implemented to get higher yield of wheat grains with good protein content. Due to morphological similarity of wild oat with wheat, this weed proved strong competitor. Therefore, it is suggested that wild oat needs to be controlled in wheat even at density of less than 5 plants m-2.