Top oil exporter Saudi Arabia may cap increases in November crude official selling prices (OSPs) to Asian customers as the shutdown of Shell\'s Singapore refinery risks reversing the bullish tone in the market over the past month. Uncertainty about the duration of the outage led to a wider range of estimates for an increase in the kingdom\'s flagship Arab Light crude of between 10 cents and $1 (Dh3.67) a barrel. The top end of the range in the Reuters survey yesterday of seven traders, including five north-east Asian buyers of Saudi crude, would price Arab Light at a record premium of $2.65 a barrel to the average of Oman/Dubai quotes, 30 cents above its previous peak for November 2007. But some traders said that an extended Shell shutdown would price out some Saudi crude should Middle East spot cargo values fall to discounts from record premiums in the past month. Regular buyer Shell\'s Singapore refinery is a regular buyer of Arab Light, a senior trading source said. \"If the OSP is too high compared to spot, people will avoid Saudi crude, so they may moderate their prices,\" said a trader with a European trading firm. Before Shell\'s accident, Middle East crude values were roaring higher, supported by strong seasonal demand across Asia ahead of the winter season. Oman crude traded at premiums of more than $2 a barrel to Dubai quotes, its highest since at least 2009, while values of the grade on the Dubai Mercantile Exchange (DME) soared well over $3. The backwardation along the Dubai swaps curve, or the premium that prompt contracts command over supplies for later delivery, steepened to the widest levels so far this year in the past few weeks and spot cargo premiums for most heavy sour grades, including Qatar Al Shaheen, reached multi-year highs. \"Everybody can expect they will increase the OSPs for every grade, especially for heavy grades,\" said a trader with a north-east Asian refiner. \"The fuel oil crack is stronger than the middle distillate crack.\" Setting the trend in the Middle East Saudi crude OSPs are usually released around the fifth of each month, and set the trend for Iranian, Kuwaiti and Iraqi prices, affecting around 8 million barrels per day (bpd) of crude bound for Asia. State oil giant Saudi Aramco sets its crude prices based on recommendations from customers and after calculating the change in the value of its oil over the past month, based on yields and product prices.