the oil composition containing at least 50 % by weight ( hereafter indicated merely by “%”) of partial glycerides used in the present invention is prepared by causing an alkali catalyst or lipase to act on an oil having the intended constitutive fatty acids and glycerol to conduct an ester exchange reaction , or by causing an alkali catalyst or lipase to act on a mixture of the intended constitutive fatty acids or esters thereof obtained by hydrolysis of an oil , and glycerol to conduct an esterification reaction . examples of the oil include vegetable oils such as soybean oil , rapeseed oil , sunflower oil , safflower oil , linseed oil , perilla oil , palm oil , rice oil and corn oil ; an animal oils such as beef tallow and fish oil ; and mixed oils , hardened oils , fractionated oils and random transesterified oils thereof . the number of carbon atoms of acyl groups constituting the partial glycerides is preferably 8 to 24 , particularly 16 to 22 . in order to lower the melting point of a liquid portion to be obtained by solid - liquid separation , the content of acyl groups derived from palmitic acid and stearic acid is preferably at most 20 %, particularly at most 15 % in total . the content of the partial glycerides in the oil composition containing the partial glycerides is at least 50 %, preferably at least 70 %, particularly higher than 80 %. the partial glycerides are preferably diglycerides , and the content of monoglycerides is preferably at most 5 %, particularly at most 2 %. the content of free fatty acids is preferably at most 5 %, particularly at most 2 % from the viewpoint of improving flavor of the oil composition . the remainder is composed of triglycerides , and the content thereof is preferably 1 to 50 %, particularly 2 to 20 % from the viewpoint of fractionation operation . an emulsifier is added to the oil composition containing at least 50 % of the partial glycerides thus prepared , and the mixture is heated , as needed , to dissolve the emulsifier in the oil composition . examples of the emulsifier used in the present invention include polyol fatty acid esters , salts of stearyl lactate , stearyl citrate , cholic acid ( salts ), etc ., with those having a melting point of 20 to 40 ° c . being preferred . particularly preferred emulsifiers are polyol fatty acid esters . examples of the polyol fatty acid esters include glycerol fatty acid monoesters , glycerol organic acid fatty acid esters ( organic acid : acetic acid , lactic acid , citric acid , succinic acid , diacetyltartaric acid or the like ), polyglycerol condensed ricinoleic acid esters , polyglycerol fatty acid esters , sucrose fatty acid esters , sorbitan fatty acid esters , polyoxyethylene sorbitan fatty acid esters , propylene glycol fatty acid esters and phospholipids , with polyglycerol fatty acid esters , sucrose fatty acid esters and sorbitan fatty acid esters being preferred . the acyl groups in the polyol fatty acid ester are saturated or unsaturated acryl groups having 12 to 22 carbon atoms , preferably 12 to 18 carbon atoms , with mixtures of the saturated and unsaturated acyl groups being particularly preferred . specifically , a mixed acyl group composed of a saturated acyl group having 12 to 18 carbon atoms and an unsaturated acyl group having 18 carbon atoms is preferred . the content of acyl groups having less than 12 carbon atoms is preferably at most 1 % based on all the constitutive acyl groups of the polyol fatty acid ester . among the polyol fatty acid esters , polyglycerol fatty acid esters are particularly preferred , with those having an average polymerization degree of 4 to 15 , preferably 8 to 12 and an esterification degree of at least 70 % being further preferred . further , the polyol fatty acid ester preferably has an hlb ( according to gfiffin &# 39 ; s equation ) of at most 7 and a melting point ranging from 20 to 40 ° c . from the viewpoint of convenient fractionation of the oil composition containing at least 50 % of the partial glycerides . with respect to the mixing proportion of the oil composition containing at least 50 % of the partial glycerides to the emulsifier , it is preferred that the emulsifier be mixed in a proportion of 0 . 001 to 5 parts by weight , preferably 0 . 05 to 0 . 5 parts by weight , particularly 0 . 1 to 0 . 3 parts by weight per 100 parts by weight of the oil composition containing the partial glycerides from the viewpoint of sure fractionation . a mixture of the oil composition containing at least 50 % of the partial glycerides and the emulsifier is then heated , as needed , to dissolve the emulsifier therein . in this case , the temperature is preferably controlled to 20 to 80 ° c ., more preferably 30 to 60 ° c . the melting point of the emulsifier , particularly , the polyol fatty acid ester used herein is preferably higher by 3 to 25 ° c ., more preferably 5 to 20 ° c . than that of the oil composition containing at least 50 % of the partial glycerides to be fractionated . the oil composition containing at least 50 % of the partial glycerides , in which the polyol fatty acid ester has been dissolved , is mixed for at least 1 minute , preferably 3 to 30 minutes in a temperature range in which no crystal is deposited , for example , at a temperature of 15 to 80 ° c ., preferably 20 to 60 ° c ., and then cooled at a cooling rate of 0 . 1 to 10 ° c ./ hr , preferably 1 to 5 ° c ./ hr , particularly 1 to 3 ° c ./ hr to deposit a high - melting diglyceride containing potion in a high - melting portion ( solid oil composition ) by the crystal - adjusting effect based on the polyol fatty acid ester , thereby growing the crystals thereof . after the temperature of the mixture reaches a temperature at which the desired high - melting portion is fully deposited , the mixture was aged for 10 to 600 minutes , preferably 30 to 300 minutes . thereafter , the high - melting portion and the low - melting portion are fractionated from the mixture by a method of filtration under pressure , vacuum filtration , centrifugation , treatment with a membrane , or the like . the method by filtration is preferred because the yield of the liquid oil composition becomes higher . as described above , the oil composition containing at least 50 % of the partial glycerides according to the present invention is preferably fractionated into solid and liquid portions without using any solvent . after a 4 - necked flask was charged with raw oil ( 2 , 500 g ), a nonselective lipase (“ lipase of ”, product of meito sangyo co ., ltd . ; 1 . 3 g ) and water ( 2 , 500 g ) to conduct hydrolysis at 40 ° c . for 6 hours with stirring under a nitrogen atmosphere , an oil phase is separated by centrifugation . this reaction product ( 2 , 000 g ) of the oil phase , glycerol ( 330 g ) and a 1 , 3 - position - selective , immobilized lipase (“ lipozyme im ”, product of novo nordisk bioindustry co . ; 200 g ) were mixed to conduct an esterification reaction for 5 hours under conditions of 40 ° c . and 4 hpa . the resultant reaction product was subjected to a molecular distillation treatment and a deodorizing treatment to obtain a partial glyceride - containing oil composition ( 1 , 360 g ) having a composition shown in table 1 . a polyol fatty acid ester ( 0 . 2 g ) or no polyol fatty acid ester was then added to portions ( each 100 g ) of the partial glyceride - containing oil composition to heat them to 40 ° c . ( to 60 ° c . in invention product 4 ), thereby preparing uniform liquids as a whole . thereafter , the liquids were cooled to 5 ° c . at a cooling rate of 2 ° c ./ hr and a stirring speed of 10 rpm and then left at rest for 2 hours . the resultant crystal slurries were separately fractionated into a solid oil composition and a liquid oil composition by a suction filtration method . the compositions of the liquid oil compositions are shown in table 2 . the invention products 1 to 5 are all liquid oil compositions , and no deposition of crystals was observed even when they were left at rest at 5 ° c . for 1 hour . in the comparative products , the crystal slurries gelled , and no liquid oil composition could not be provided . therefore , the partial glyceride - containing oil compositions shown in table 1 were respectively stored at 5 ° c . as a result , both oil compositions derived from sunflower oil and soybean oil deposited crystals at 5 ° c . to gel . in particular , the oil composition making use of soybean oil was solidified in a bottle for salad oil and could not be taken out of the bottle . sunflower oil ( 81 parts by weight ) as a raw oil was added to the partial glyceride - containing oil composition ( 29 parts by weight ) derived from sunflower oil shown in table 1 to prepare an oil composition containing 25 % of diglycerides . the above - described synthetic product ( 0 . 2 g ) of the polyol fatty acid ester was added to this oil composition ( 100 g ), and the mixture was heated to 40 ° c ., thereby preparing a uniform liquid as a whole . thereafter , the liquid was cooled at a cooling rate of 2 ° c ./ hr and a stirring speed of 10 rpm . since this oil composition contained about 74 % of triglycerides , the melting point thereof was low , and so no crystal was deposited by − 4 ° c . therefore , the liquid was cooled to − 10 ° c . and then left at rest for 2 hours . the resultant crystal slurry gelled , and crystals thereof were too fine to collect them by filtration . as described above , according to the present invention , oil compositions comprising at least 50 % of partial glycerides can be easily fractionated into a solid oil composition and a liquid oil composition .