برآورد کشش محصولات نفتی تقاضا در نیجریه:روش هم انباشتگی چندمتغیره

This paper formulates and estimates petroleum products demand functions in Nigeria at both aggregative and product level for the period 1977 to 2006 using multivariate cointegration approach. The estimated short and long-run price and income elasticities confirm conventional wisdom that energy consumption responds positively to changes in GDP and negatively to changes in energy price. However, the price and income elasticities of demand varied according to product type. Kerosene and gasoline have relatively high short-run income and price elasticities compared to diesel. Overall, the results show petroleum products to be price and income inelastic.

Energy demand modelling has focused on improving our understanding of the size and dynamics of consumer responses to changes in relative energy prices and the level of economic activity since the price of oil quadrupled in the early 1970s (Bohi and Zimmerman, 1984, Gately, 1993, Dahl, 1994 and Liu, 2004). Nevertheless, the quest for more accurate estimates of key energy demand parameters such as short and long-run price and income elasticities derives from three factors. First is their critical importance in the projection of future energy demand in particular, and energy market trends in general. Second is the role of these parameters in the design of policies for dealing with the negative environment externalities of the energy sector. Third is the fact that understanding energy demand dynamics through improved and more robust estimates of energy demand parameters is essential for more informed and successful energy policy decision making and implementation. Often times and for various reasons, unduly strong assumptions have been made in the estimation of these elasticities in many developing countries. The implications of these strong assumptions are hardly alluded to in drawing conclusions from the estimated results. In many cases, the estimated models are likely to have produced spurious parameter results. Obviously, policies based on such parameters are more likely to result in wrong policy actions. The key objective of this paper therefore is to model and estimate petroleum products demand dynamics in Nigeria based on a multivariate cointegration approach with the aim of deriving improved and more robust estimates of price and income elasticities. In the process, we investigate whether there is a long-run relationship between petroleum product demand and its primary determinants, price and income. In this empirical exploration we attempt to fill an important gap in the empirical literature on developing countries. This study is the first rigorous econometric study of Nigeria's energy demand function at the aggregated level and by energy type. Also the paper examines the time-series properties of the data series with a view to minimizing spurious regression results associated with a less rigorous econometric approach. The data for the study covers the period 1977 to 2006.3 The structure of the paper is as follows. In Section 2 we present some stylized facts about petroleum products and the Nigerian economy. Section 3 presents a brief review of the literature. Section 4 discusses the analytical framework on which the model is predicated while Section 5 discusses estimation issues. The main empirical findings and their policy implications are discussed in Section 6. The conclusions and policy implications are presented in Section 7.

In this study we examined the price and income elasticity of energy demand in Nigeria at aggregate level and by product type over the period (1977 to 2006). Our results show that aggregate petroleum products demand in Nigeria conform with a priori expectations of negative price elasticity and positive income elasticity. Price and income elasticities of demand for petroleum products however vary reflecting the difference in services provided by the various fuels. Among the petroleum products, gasoline has the highest income elasticity followed by kerosene. In a similar vein, kerosene has the highest price elasticity followed by diesel in absolute terms. Energy prices and income are therefore major factors influencing the demand for energy in Nigeria. The results also show that the short-run and long-run elasticities were generally less than unity i.e. they have inelastic demand. Furthermore, while per capita income can be said to have significant impact on future changes in aggregate petroleum products and gasoline demand, the real prices of diesel and kerosene exert significant influence on the future changes of diesel and kerosene in Nigeria. The coefficients of the error-correction term for the various models indicate that adjustments in aggregate petroleum products demand and in petroleum products occur within one year. Our findings appear to have significant policy implications for an oil producing economy such as Nigeria, particularly with respect to the way in which taxation could help the government increase fiscal revenues and regulate the level and/or structure of energy consumption. The responsiveness of petroleum products demand to price changes suggests that taxes on their own are likely to achieve government goals for energy conservation or environmental improvement, and they may well be efficient for revenue raising. Given the nature of the petroleum products, Nigeria can conveniently embark on policy measures that lead to price increase (such as increase petroleum prices) in order to raise revenue. This is because consumers' response, of reducing consumption, to the price increase will be low and the final outcome is an increase in the total government revenue.