國際原油對國內車用汽油價格之不對稱衝擊效果評估

Testing for Asymmetric Pricing in the Taiwan Gasoline Market

林灼榮(Jwu-Rong Lin) ； 劉浩然(Hao-Ran Liou)

《農業與資源經濟》 6卷2期 (2009/12) Pp. 71-101

https://doi.org/10.29796/ARE.200912.0003

摘要

台灣是個高度仰賴能源進口之國家，對原油進口依存度接近100%，近來國際油價大幅上漲，這種全球性石油衝擊效應，使得國內油價跟著調漲而加重車用汽油消費者之負擔；然而，國內油品市場雙龍頭中油及台塑，其調價行爲是否與原油價格同步，係社會大眾所極力關注之議題；故本文擬剖析國內外油價漲跌訊息，並進一步檢證國內油品價格相對於國際油價，是否呈現漲多跌少之不對稱議題。本文利用2000 年12月31日至2006年12月31日（浮動油價前），共計313筆週資料，建構不對稱誤差修正模型(Asymmetric Error Correction Model, AECM)，並以表面無關聯立迴歸法(Seemingly Unrelated Regression Method, SUR)，檢證國際原油價格、國內中油及台塑95汽油之批發價格、國內95汽油零售價格，其漲跌幅是否存在漲多跌少之不對稱現象。實證結果發現：(1)由誤差修正係數之實證結果，發現國際油價與國內零售價之漲幅衝擊係數大於跌幅，然而在國內批發價方面，則呈現跌幅係數大於漲幅係數現象，但若進一步由漲跌幅係數之相對差距檢定，則國內油價誤差修正係數之差距顯著小於國際油價；換言之，當國內外油價由短期邁向長期均衡之動態歷程中，並沒有充分證據支持國內油價相對於國際油價，呈現調漲速度大於降價速度現象。(2)由落遲1~5及7期之迴歸係數集體檢定結果，發現國際油價單向顯著影響國內油價，顯示台灣在原油進口上屬於價格接受者之貿易小國特性。(3)中油與台塑批發價，呈現雙向因果關係，且二者對零售價皆具影響力；此等訊息，顯示台灣車用汽油市場，呈現兩家互爲領導者之壟斷現象。(4)歸納本文實證結果，發現國內外油品本身大抵存在漲多跌少之不對稱訊息，但國內油價之漲跌幅差距並沒有明顯高於國際油價；換言之，國內油品價格在管制式訂價下，相對於國際油價，並沒有明顯呈現漲多跌少而不利於車用消費者之證據。

關鍵字

國際原油價格 ； 漲跌不對稱 ； 不對稱誤差修正模型

並列摘要

Taiwan is highly dependent on energy imports, especially crude oil. In recent years, crude oil prices have risen fiercely, and had a serious impact on domestic gasoline prices and the economy. Chinese Petroleum Corp. (CPC) and Formosa Petrochemical Corp. (FPCC) make up the entire gasoline market in Taiwan. In this context, whether domestic gasoline wholesale prices and retail prices adjust at the same pace as international crude oil prices is the main subject this research is attempting to identify. The research applies an Asymmetric Error Correction Model to examine the issue of asymmetries in the transmission of shocks to crude oil prices onto wholesale and retail gasoline prices, using weekly data for the period from December 2000 to December 2006. The results show that there have been more rises than falls in the international and domestic retail oil market. Moreover a long-term cointegrating relationship exists between crude oil price and domestic gasoline prices. Additionally, we find evidence of gasoline price asymmetries if we adopt WTI as the indicator in a floating oil pricing mechanism, but the degree of asymmetries on domestic prices are smaller than international prices. Finally, the retail gasoline price is affected by international oil prices and wholesale gasoline prices. In a duopoly gasoline wholesale market, the pricing strategies of both CPC and FPCC are cooperative.

並列關鍵字

International Crude Oil ； Rise and Fall Asymmetry ； Asymmetric Error Correction Model