$re = '/\s?on\w+="[^"]+"\s?/';
$str = '<body>
<script src="...">
</script>
<div onresize="CreateFixedHeaders()" onscroll="CreateFixedHeaders()" id="oReportDiv" style="overflow:auto;WIDTH:100%">
<script type="text/javascript" language="javascript">
//<![CDATA[
function CreateFixedHeaders() {}//]]>
</script>
<script>
var ClientReportfb64a4706a3749c484169e...
</script>
</body>';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php