**Update 2: ** After changing my location line to location ^~ /classifieds/, we finally were able to get the rewrites working, but were experiencing a redirect loop. As an example, the URL /classifieds/g2-general-category.html was properly being rewritten to /classifieds/showcat.php?cat=2 but it appears that the script was detecting this rewrite and attempting to send the user to the proper SEO URL, which rewrote to showcat.php, ad infinitum. Additionally, after the rewrite loop was finished, my browser URL bar would indicate showcat.php 50% of the time and g2-general-category.html the other 50% of the time. So I guess my question is - How can we avoid this behavior? To my untrained eye, it looks like what is happening is that:

User visits g2-general-category.html. nginx sends user to showcat.php?cat=2 PHP script sees that user is not using the SEO'd URL, so does a header redirect to send them to the correct URL, where nginx then rewrites it to showcat.php?cat=2 again.

**Update: ** Following is some more (hopefully) useful information. When requesting a URL, the logs indicate that the 404 is happening before the rewrite takes place:

2013/03/11 10:38:18 [error] 10073#0: *13003643 open() "/home/site/public_html/classifieds/category-name-here/p1097-product.html" failed (2: No such file or directory), client: IP, server: site.com, request: "GET /classifieds/category-name-here/p1097-product.html HTTP/1.1", host: "www.site.com" 

The full configuration file is below:

server { server_name site.com www.site.com; root "/home/site/public_html"; index index.php; client_max_body_size 10m; access_log /home/site/_logs/access.log; error_log /home/site/_logs/error.log; location /classifieds/ { rewrite ^/classifieds/(.*)/p([0-9]+)-(.*)-page([0-9+]).html$ /classifieds/showproduct.php?product=$2&cpage=$4 permanent; rewrite ^/classifieds/(.*)/p([0-9]+)-(.*).html$ /classifieds/showproduct.php?product=$2 permanent; rewrite ^/classifieds/(.*)/p([0-9]+).html$ /classifieds/showproduct.php?product=$2 permanent; rewrite ^/classifieds/g([0-9]+)-(.*)-page([0-9]+).html$ /classifieds/showcat.php?cat=$1&page=$3 permanent; rewrite ^/classifieds/g([0-9]+)-(.*).html$ /classifieds/showcat.php?cat=$1 permanent; rewrite ^/classifieds/(.*)/index([0-9]+)-([0-9]+).html$ /classifieds/index.php?cat=$2&page=$3 permanent; rewrite ^/classifieds/(.*)/index([0-9]+).html$ /classifieds/index.php?cat=$2 permanent; rewrite ^/classifieds/m([0-9]+)-(.*)-protype([0-9]+).html$ /classifieds/member.php?uid=$1&protype=$3 permanent; rewrite ^/classifieds/m([0-9]+)-(.*).html$ /classifieds/member.php?uid=$1 permanent; rewrite ^/classifieds/board.html$ /classifieds/board.php permanent; rewrite ^/classifieds/b([0-9]+)-(.*).html$ /classifieds/board.php?msg=$1 permanent; rewrite ^/classifieds/u([0-9]+)-(.*)-page([0-9]+).html$ /classifieds/showcat.php?ppuser=$1&page=$3 permanent; rewrite ^/classifieds/u([0-9]+)-(.*).html$ /classifieds/showcat.php?ppuser=$1 permanent; rewrite ^/classifieds/s([0-9]+)-(.*)-page([0-9]+).html$ /classifieds/showmembers.php?cat=$1&page=$3 permanent; rewrite ^/classifieds/s([0-9]+)-(.*).html$ /classifieds/showmembers.php?cat=$1 permanent; } location / { try_files $uri $uri/ /index.php$uri?$args; } location ~ "^(.+\.php)($|/)" { fastcgi_split_path_info ^(.+\.php)(.*)$; fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name; fastcgi_param SCRIPT_NAME $fastcgi_script_name; fastcgi_param PATH_INFO $fastcgi_path_info; fastcgi_param SERVER_NAME $host; if ($uri !~ "^/uploads/") { fastcgi_pass 127.0.0.1:9006; } include fastcgi_params; } location ~* \.(js|css|png|jpg|jpeg|gif|ico)$ { expires max; log_not_found off; access_log off; } location ~* \.(html|htm)$ { expires 30m; } location ~* /\.(ht|git|svn) { deny all; } }