A small slash in petrol price is awaiting the customers before this Diwali. There may be Rs 1.50 cut in petrol price per litre as favourable changes in the rupee-dollar rate and softer international prices have set the tone in the direction.    Petrol companies decreased petrol rates by Rs 3.66 a litre in New Delhi last month after nine successive hikes in four months. The fuel rate was cut sharply after benchmark international gasoline rates dropped by $4 per barrel to $113 and the currency appreciated by Rs 3 to 63 per dollar.    As per the media reports, a preliminary analysis of pricing data shows about $1 drop in the international gasoline rate and little less than $1 gain in exchange rate. Together, inclusive of state levies in Delhi, the price reduction should be around Rs 1.26 per litre.    Sources concerned said that price cut will be more if average gasoline price drop further and rupee appreciates in next two days.