I am not too sure on this one - so instead of answereing the question, I hopefully initiate a discussion, the end of which should reveal the answer..... I see it like this: In any time frame, if the close is less than the close of the previous bar, the OBV will be negative. Lets look at an hourly chart: if the price action during the day was such:

Time Open Close
10:00 10.00 9.00
11:00 9.00 8.00
12:00 8.00 7.00
13:00 7.00 6.00
14:00 6.00 5.00
15:00 5.00 4.00

During each hour the price fell, and as such the OBV would be negative for all of the values, except maybe the first hour of the day (we look at the first hour shortly) What is the closing price from the previous day was 3.00 ? The first hour OBV would be positive. BUT the daily OBV would also be positive because todays close is greater than yesterdays close. Is this right? In this example, not every daily bar has a negative affect on the OBV and I cannot think of a situation where it is possible, but then again I havent had my morning coffee yet either! Hope this helps. wabbit :D