What Are The Factors Determining Demand?

Supply is a big one as is need and cost.

Factors determining demand are as follows- consumers income,taxation,population , taste and fashion,band-wagon effect e.t.c.

I am not an expert in this area but I think that the current low oil prices are an example of demand affecting price, according to the experts.
The slow economy worldwide is creating less demand for oil because production is down.  In addition, the slow economy is causing workers to lose their jobs so they don't buy gas to go to work nor to shop. So, how businesses are doing may affect the demand for products made by other businesses and it becomes a snowball effect. Also, disposable income affects the amount of retail and other purchases.  There are many examples of factors affecting demand in this current economy.

Factors that determine the value of price elasticity of demand
1. Number of close substitutes within the market - The more (and closer) substitutes available in the market the more elastic demand will be in response to a change in price. In this case, the substitution effect will be quite strong.
2. Luxuries and necessities - Necessities tend to have a more inelastic demand curve, whereas luxury goods and services tend to be more elastic. For example, the demand for opera tickets is more elastic than the demand for urban rail travel. The demand for vacation air travel is more elastic than the demand for business air travel.
3. Percentage of income spent on a good - It may be the case that the smaller the proportion of income spent taken up with purchasing the good or service the more inelastic demand will be.
4. Habit forming goods - Goods such as cigarettes and drugs tend to be inelastic in demand. Preferences are such that habitual consumers of certain products become de-sensitised to price changes.
5. Time period under consideration - Demand tends to be more elastic in the long run rather than in the short run. For example, after the two world oil price shocks of the 1970s - the "response" to higher oil prices was modest in the immediate period after price increases, but as time passed, people found ways to consume less petroleum and other oil products. This included measures to get better mileage from their cars; higher spending on insulation in homes and car pooling for commuters. The demand for oil became more elastic in the long-run.