It's quite hard for me to get across the slightly differing sounds as it'snot my native tongue. That is why I used "approximation" in my comment, but yes it does seem like an ever lengthening ee sound. The rule is that if the vowel is followed by a double consonant it's a short vowel, single consonant means long vowel, so bil = beel and bill = beeel. But as a non-native it can be very hard to distinguish during a conversation and I am often misunderstood. In fact, I'm not even sure I have the rule the right way around :(